AssetManager: Use directory name without trailing slash when calling AssetManager.list()

It seems that earlier version of Android (probably Android 8) returns empty files if the
passed path in AssetManager.list() contains trailing slash.

love/src/main/java/org/love2d/android/GameActivity.java

@@ -557,9 +557,9 @@ public class GameActivity extends SDLActivity {
 
             // List files
             try {
-                list = assetManager.list(dir);
+                list = assetManager.list(strippedDir);
             } catch (IOException e2) {
-                Log.e("GameActivity", dir, e2);
+                Log.e("GameActivity", strippedDir, e2);
             }
 
             // Mark as file