ffmpeg_source: add url check to android_open

This check confirms that if a URL is attached to the
android-source in the url string passed to android_open,
that it match the actual URL pointed to by that datasource.

It has been observed that some hls,applehttp sources contain
playlists within the playlist. In these cases, the additional
playlists may be opened by rewriting the original URL. However,
since the "android-source:<%p>" prefix is unmodified, it "opens"
the original URL again. This continues until memory is depleted.

Change-Id: Ieb504393aaa204a641035c982fe4a123a3e61a98