Fix for build fails when no java files to copy. 

Commit https://github.com/kivy/python-for-android/commit/668cedc7b07ce20a98e787941b379c0f81a13e8a
introduced line 551 which had a try clause before it copied java files, but often there are no java files to copy. This would cause the build to fail. I removed the try clause so the build will continue whether there are java files to copy or not.