avcodec/g2meet: fix error returns

Fixes out of array accesses

This should not affect any release

Fixes: 8ab69af9e5a7a7e20fe04cdd25c0d6e7-asan_heap-oob_e72b82_5505_cov_2278389485_g2m4.wmv
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 6b53c1aa)

Conflicts:

	libavcodec/g2meet.c

libavcodec/g2meet.c

@@ -709,7 +709,8 @@ static int g2m_decode_frame(AVCodecContext *avctx, void *data,
                 av_log(avctx, AV_LOG_ERROR,
                        "Unknown compression method %d\n",
                        c->compression);
-                return AVERROR_PATCHWELCOME;
+                ret = AVERROR_PATCHWELCOME;
+                goto header_fail;
             }
             c->tile_width  = bytestream2_get_be32(&bc);
             c->tile_height = bytestream2_get_be32(&bc);