Bug 878392 - Reset Decoder::mCurrentFrame to nullptr if we fail to create a frame. r=seth

--HG--
extra : rebase_source : 1188bfd4896c687eb954ac781cd23e2d49a48959
Bug 878751 - Port a bug fix from Chrome back to Mozilla. r=jlebar

--HG--
extra : rebase_source : d680dada2ac1932806e10c6050376a849112f523