Do not read theme twice if format is predefined

vtm-themes/src/org/oscim/theme/VtmThemes.java

@@ -3,6 +3,7 @@
  * Copyright 2013 Hannes Janetzek
  * Copyright 2016-2017 devemux86
  * Copyright 2017 nebular
+ * Copyright 2017 Andrey Novikov
  *
  * This file is part of the OpenScienceMap project (http://www.opensciencemap.org).
  *
@@ -58,6 +59,11 @@ public enum VtmThemes implements ThemeFile {
         return AssetAdapter.readFileAsStream(mPath);
     }
 
+    @Override
+    public boolean isMapsforgeTheme() {
+        return false;
+    }
+
     @Override
     public void setMenuCallback(XmlRenderThemeMenuCallback menuCallback) {
     }