Fix: Behandle leere Nextcloud-Dateien korrekt

- Aendert loadFile(): Gibt leeres Array zurueck, wenn Datei existiert aber leer ist
- Verhindert, dass leere Dateien als null interpretiert werden und lokale Daten
  oder leere Arrays geladen werden

Fixes: Datenverlust bei Nextcloud-Anmeldung mit leeren Dateien

Co-authored-by: trevor1969 <trevor1969@users.noreply.github.com>

app.js

@@ -135,7 +135,8 @@ class NextcloudStorage {
 
             if (response.ok) {
                 const text = await response.text();
-                return text ? JSON.parse(text) : null;
+                // Return empty array if file is empty, otherwise parse JSON
+                return text.trim() === '' ? [] : (text ? JSON.parse(text) : null);
             } else if (response.status === 404) {
                 return null;
             }
@@ -280,13 +281,31 @@ class TeeTracker {
             const teas = await this.nextcloudStorage.loadFile(DATA_DIRECTORY + 'teas.json');
             const entries = await this.nextcloudStorage.loadFile(DATA_DIRECTORY + 'entries.json');
             
-            // Load from Nextcloud if available
+            // Always load from localStorage first as backup
+            const localTeas = localStorage.getItem(STORAGE_KEY_TEAS);
+            const localEntries = localStorage.getItem(STORAGE_KEY_ENTRIES);
+            
+            // Load from Nextcloud if available, otherwise use local data
             if (teas) {
                 this.teas = teas.map(tea => ({
                     ...tea,
                     organic: tea.organic !== undefined ? tea.organic : false,
                     rating: tea.rating !== undefined ? tea.rating : 3
                 }));
+            } else if (localTeas) {
+                // Nextcloud has no teas, use local data
+                try {
+                    this.teas = JSON.parse(localTeas).map(tea => ({
+                        ...tea,
+                        organic: tea.organic !== undefined ? tea.organic : false,
+                        rating: tea.rating !== undefined ? tea.rating : 3
+                    }));
+                } catch (error) {
+                    console.error('Error loading local teas:', error);
+                    this.teas = [];
+                }
+            } else {
+                this.teas = [];
             }
             
             if (entries) {
@@ -294,40 +313,19 @@ class TeeTracker {
                     ...entry,
                     teaspoons: entry.teaspoons !== undefined ? entry.teaspoons : 1
                 }));
-            }
+            } else if (localEntries) {
-            
+                // Nextcloud has no entries, use local data
-            // If any data is missing from Nextcloud, load from localStorage
+                try {
-            // This prevents data loss when switching to Nextcloud
+                    this.entries = JSON.parse(localEntries).map(entry => ({
-            if (!teas && !entries) {
+                        ...entry,
-                // Both Nextcloud files are missing, load everything from localStorage
+                        teaspoons: entry.teaspoons !== undefined ? entry.teaspoons : 1
-                this.loadFromLocalStorage();
+                    }));
-            } else if (!teas) {
+                } catch (error) {
-                // Only teas.json is missing from Nextcloud, load teas from localStorage
+                    console.error('Error loading local entries:', error);
-                const localTeas = localStorage.getItem(STORAGE_KEY_TEAS);
+                    this.entries = [];
-                if (localTeas) {
-                    try {
-                        this.teas = JSON.parse(localTeas).map(tea => ({
-                            ...tea,
-                            organic: tea.organic !== undefined ? tea.organic : false,
-                            rating: tea.rating !== undefined ? tea.rating : 3
-                        }));
-                    } catch (error) {
-                        console.error('Error loading local teas:', error);
-                    }
-                }
-            } else if (!entries) {
-                // Only entries.json is missing from Nextcloud, load entries from localStorage
-                const localEntries = localStorage.getItem(STORAGE_KEY_ENTRIES);
-                if (localEntries) {
-                    try {
-                        this.entries = JSON.parse(localEntries).map(entry => ({
-                            ...entry,
-                            teaspoons: entry.teaspoons !== undefined ? entry.teaspoons : 1
-                        }));
-                    } catch (error) {
-                        console.error('Error loading local entries:', error);
-                    }
                 }
+            } else {
+                this.entries = [];
             }
         } else {
             // Load from localStorage