Add another safeguard to prevent unintended slf4j setup

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/Logging.java

@@ -61,6 +61,10 @@ public abstract class Logging {
             return null;
     }
 
+    public boolean isFileLoggerInitialized() {
+        return fileLogger != null;
+    }
+
     public void debugLoggingConfiguration() {
         // For debugging problems with the logback configuration
         LoggerContext lc = (LoggerContext) LoggerFactory.getILoggerFactory();

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/GB.java

@@ -31,6 +31,7 @@ import android.os.Handler;
 import android.os.Looper;
 import android.text.Html;
 import android.text.SpannableString;
+import android.util.Log;
 import android.widget.Toast;
 
 import androidx.annotation.NonNull;
@@ -98,6 +99,8 @@ public class GB {
 
     private static boolean notificationChannelsCreated;
 
+    private static final String TAG = "GB";
+
     public static void createNotificationChannels(Context context) {
         if (notificationChannelsCreated) return;
 
@@ -459,6 +462,18 @@ public class GB {
     }
 
     public static void log(String message, int severity, Throwable ex) {
+
+        // Handle if slf4j is not setup yet as this causes this issue:
+        // https://codeberg.org/Freeyourgadget/Gadgetbridge/issues/2394
+        // and similar, as reported by users via matrix chat, because
+        // under some conditions the FileUtils.getWritableExternalFilesDirs
+        // can break the slf4j rule again, but this method is used while bootstrapping
+        // slf4j, so catch22... and it is useful to have proper logging when slf4f is ready.
+        if (!GBApplication.getLogging().isFileLoggerInitialized()) {
+            Log.i(TAG, message);
+            return;
+        }
+
         switch (severity) {
             case INFO:
                 LOG.info(message, ex);