avcodec/movtextdec: Reset counter of fonts when freeing them

If allocating fonts fails when reading the header, all fonts are freed,
yet the counter of fonts is not reset and no error is returned; when
subtitles are decoded lateron, the inexistent list of fonts is searched
for the matching font for this particular entry which of course leads to
a segfault.

Reviewed-by: Philip Langdale <philipl@overt.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/movtextdec.c

@@ -148,6 +148,7 @@ static void mov_text_cleanup_ftab(MovTextContext *m)
         }
     }
     av_freep(&m->ftab);
+    m->ftab_entries = 0;
 }
 
 static int mov_text_tx3g(AVCodecContext *avctx, MovTextContext *m)
@@ -230,7 +231,6 @@ static int mov_text_tx3g(AVCodecContext *avctx, MovTextContext *m)
         box_size += 3;
         if (avctx->extradata_size < box_size) {
             mov_text_cleanup_ftab(m);
-            m->ftab_entries = 0;
             return -1;
         }
         m->ftab_temp = av_mallocz(sizeof(*m->ftab_temp));
@@ -245,7 +245,6 @@ static int mov_text_tx3g(AVCodecContext *avctx, MovTextContext *m)
         box_size = box_size + font_length;
         if (avctx->extradata_size < box_size) {
             mov_text_cleanup_ftab(m);
-            m->ftab_entries = 0;
             return -1;
         }
         m->ftab_temp->font = av_malloc(font_length + 1);