Revert 70077 - Don't uninitialize FFmpegVideoDecodeEngine if we haven't initialized it.

      BUG=67303
TEST=media_unittests

Review URL: http://codereview.chromium.org/6046006

TBR=scherkus@chromium.org
Review URL: http://codereview.chromium.org/5970011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@70092 0039d316-1c4b-4281-b951-d872f2087c98