avcodec/ffv1: Simplify cleanup after allocation failure

Now that ff_ffv1_close() is called upon failure for both the FFV1 encoder
and decoder, the code contained therein can be used to free the partially
allocated slice contexts if allocating the slice contexts failed. One just
has to set the correct number of slice contexts on error. This allows to
remove the code for freeing partially allocated slice contexts in
ff_ffv1_init_slice_contexts().

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/ffv1.c

@@ -119,7 +119,7 @@ av_cold int ff_ffv1_init_slice_contexts(FFV1Context *f)
 
     av_assert0(max_slice_count > 0);
 
-    for (i = 0; i < max_slice_count; i++) {
+    for (i = 0; i < max_slice_count;) {
         int sx          = i % f->num_h_slices;
         int sy          = i / f->num_h_slices;
         int sxs         = f->avctx->width  *  sx      / f->num_h_slices;
@@ -131,7 +131,7 @@ av_cold int ff_ffv1_init_slice_contexts(FFV1Context *f)
         if (!fs)
             goto memfail;
 
-        f->slice_context[i] = fs;
+        f->slice_context[i++] = fs;
         memcpy(fs, f, sizeof(*fs));
         memset(fs->rc_stat2, 0, sizeof(fs->rc_stat2));
 
@@ -144,22 +144,14 @@ av_cold int ff_ffv1_init_slice_contexts(FFV1Context *f)
                                       sizeof(*fs->sample_buffer));
         fs->sample_buffer32 = av_malloc_array((fs->width + 6), 3 * MAX_PLANES *
                                         sizeof(*fs->sample_buffer32));
-        if (!fs->sample_buffer || !fs->sample_buffer32) {
-            av_freep(&fs->sample_buffer);
-            av_freep(&fs->sample_buffer32);
-            av_freep(&f->slice_context[i]);
+        if (!fs->sample_buffer || !fs->sample_buffer32)
             goto memfail;
-        }
     }
     f->max_slice_count = max_slice_count;
     return 0;
 
 memfail:
-    while(--i >= 0) {
-        av_freep(&f->slice_context[i]->sample_buffer);
-        av_freep(&f->slice_context[i]->sample_buffer32);
-        av_freep(&f->slice_context[i]);
-    }
+    f->max_slice_count = i;
     return AVERROR(ENOMEM);
 }