avcodec/ansi: Fix frame memleak

Fixes: 1892/clusterfuzz-testcase-minimized-4519341733183488

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit e091b9b3c7)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ansi.c

@@ -80,10 +80,6 @@ static av_cold int decode_init(AVCodecContext *avctx)
     AnsiContext *s = avctx->priv_data;
     avctx->pix_fmt = AV_PIX_FMT_PAL8;
 
-    s->frame = av_frame_alloc();
-    if (!s->frame)
-        return AVERROR(ENOMEM);
-
     /* defaults */
     s->font        = avpriv_vga16_font;
     s->font_height = 16;
@@ -98,6 +94,11 @@ static av_cold int decode_init(AVCodecContext *avctx)
         av_log(avctx, AV_LOG_ERROR, "Invalid dimensions %d %d\n", avctx->width, avctx->height);
         return AVERROR(EINVAL);
     }
+
+    s->frame = av_frame_alloc();
+    if (!s->frame)
+        return AVERROR(ENOMEM);
+
     return 0;
 }