avcodec/xsubdec: Cleanup generically upon allocation error

This is possible by incrementing the counter of allocated rects
directly after said allocation succeeded.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/xsubdec.c

@@ -101,10 +101,9 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_sub_ptr,
         return AVERROR(ENOMEM);
 
     sub->rects[0] = av_mallocz(sizeof(*sub->rects[0]));
-    if (!sub->rects[0]) {
-        av_freep(&sub->rects);
+    if (!sub->rects[0])
         return AVERROR(ENOMEM);
-    }
+    sub->num_rects = 1;
     sub->rects[0]->x = x; sub->rects[0]->y = y;
     sub->rects[0]->w = w; sub->rects[0]->h = h;
     sub->rects[0]->type = SUBTITLE_BITMAP;
@@ -112,14 +111,8 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_sub_ptr,
     sub->rects[0]->data[0] = av_malloc(w * h);
     sub->rects[0]->nb_colors = 4;
     sub->rects[0]->data[1] = av_mallocz(AVPALETTE_SIZE);
-    if (!sub->rects[0]->data[0] || !sub->rects[0]->data[1]) {
-        av_freep(&sub->rects[0]->data[1]);
-        av_freep(&sub->rects[0]->data[0]);
-        av_freep(&sub->rects[0]);
-        av_freep(&sub->rects);
+    if (!sub->rects[0]->data[0] || !sub->rects[0]->data[1])
         return AVERROR(ENOMEM);
-    }
-    sub->num_rects = 1;
 
     // read palette
     for (i = 0; i < sub->rects[0]->nb_colors; i++)