Fix memory leaks on failed ff_h264_decode_init()

During failure conditions ff_h264_decode_init() leaks memory
allocated for nal units.  Found via valgrind.

Valgrind traces: http://pastebin.com/GqTqxs8T

Signed-off-by: Dale Curtis <dalecurtis@chromium.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/h264.c

@@ -1251,8 +1251,10 @@ av_cold int ff_h264_decode_init(AVCodecContext *avctx)
     }
 
     if (avctx->extradata_size > 0 && avctx->extradata &&
-        ff_h264_decode_extradata(h, avctx->extradata, avctx->extradata_size) < 0)
+        ff_h264_decode_extradata(h, avctx->extradata, avctx->extradata_size) < 0) {
+        ff_h264_free_context(h);
         return -1;
+    }
 
     if (h->sps.bitstream_restriction_flag &&
         s->avctx->has_b_frames < h->sps.num_reorder_frames) {