Allow clearing Google backup

app/src/main/java/eu/faircode/email/FairEmailBackupAgent.java

@@ -65,12 +65,10 @@ public class FairEmailBackupAgent extends BackupAgent {
 
             EntityLog.log(this, "Backup start enabled=" + enabled);
 
-            if (!enabled)
-                return;
-
             JSONObject jroot = new JSONObject();
             jroot.put("version", 1);
 
+            if (enabled) {
                 JSONObject jsettings = new JSONObject();
                 jsettings.put("enabled", prefs.getBoolean("enabled", true));
                 jsettings.put("poll_interval", prefs.getInt("poll_interval", 0));
@@ -108,6 +106,7 @@ public class FairEmailBackupAgent extends BackupAgent {
                         Log.e(ex);
                     }
                 jroot.put("accounts", jaccounts);
+            }
 
             byte[] dataBuf = jroot.toString().getBytes(StandardCharsets.UTF_8);
             String dataHash = Helper.sha256(dataBuf);
@@ -153,14 +152,11 @@ public class FairEmailBackupAgent extends BackupAgent {
     @Override
     public void onRestore(BackupDataInput data, int appVersionCode, ParcelFileDescriptor newState) {
         try {
+            EntityLog.log(this, "Restore start version=" + appVersionCode);
+
             SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
             boolean enabled = prefs.getBoolean("google_backup", BuildConfig.PLAY_STORE_RELEASE);
 
-            EntityLog.log(this, "Restore start enabled=" + enabled + " version=" + appVersionCode);
-
-            if (!enabled)
-                return;
-
             while (data.readNextHeader()) {
                 String dataKey = data.getKey();
                 int dataSize = data.getDataSize();
@@ -181,6 +177,11 @@ public class FairEmailBackupAgent extends BackupAgent {
                         JSONObject jroot = new JSONObject(new String(dataBuf, StandardCharsets.UTF_8));
                         EntityLog.log(this, "Restore version=" + jroot.optInt("version", 0));
 
+                        if (!enabled || !jroot.has("accounts")) {
+                            EntityLog.log(this, "Restore empty or disabled");
+                            continue;
+                        }
+
                         SharedPreferences.Editor editor = prefs.edit();
                         JSONObject jsettings = jroot.getJSONObject("settings");
                         editor.putBoolean("enabled", jsettings.optBoolean("enabled"));