Do not read theme twice if format is predefined

vtm-android/src/org/oscim/android/theme/AssetsRenderTheme.java

@@ -1,6 +1,7 @@
 /*
  * Copyright 2010, 2011, 2012 mapsforge.org
  * Copyright 2016-2017 devemux86
+ * Copyright 2017 Andrey Novikov
  *
  * This program is free software: you can redistribute it and/or modify it under the
  * terms of the GNU Lesser General Public License as published by the Free Software
@@ -20,6 +21,7 @@ import android.text.TextUtils;
 
 import org.oscim.theme.IRenderTheme.ThemeException;
 import org.oscim.theme.ThemeFile;
+import org.oscim.theme.ThemeUtils;
 import org.oscim.theme.XmlRenderThemeMenuCallback;
 import org.oscim.utils.Utils;
 
@@ -98,6 +100,11 @@ public class AssetsRenderTheme implements ThemeFile {
         }
     }
 
+    @Override
+    public boolean isMapsforgeTheme() {
+        return ThemeUtils.isMapsforgeTheme(this);
+    }
+
     @Override
     public void setMenuCallback(XmlRenderThemeMenuCallback menuCallback) {
         mMenuCallback = menuCallback;