set pragme secure delete properly

src/main/java/eu/siacs/conversations/persistance/DatabaseBackend.java

@@ -190,7 +190,7 @@ public class DatabaseBackend extends SQLiteOpenHelper {
 	@Override
 	public void onConfigure(SQLiteDatabase db) {
 		db.execSQL("PRAGMA foreign_keys=ON");
-		db.execSQL("PRAGMA secure_delete=ON");
+		db.rawQuery("PRAGMA secure_delete=ON",null);
 	}
 
 	@Override