avfilter/vf_drawtext: fix resource leaks

Fixes CID1206649
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/vf_drawtext.c

@@ -457,6 +457,7 @@ static int load_textfile(AVFilterContext *ctx)
     DrawTextContext *s = ctx->priv;
     int err;
     uint8_t *textbuf;
+    uint8_t *tmp;
     size_t textbuf_size;
 
     if ((err = av_file_map(s->textfile, &textbuf, &textbuf_size, 0, ctx)) < 0) {
@@ -466,8 +467,11 @@ static int load_textfile(AVFilterContext *ctx)
         return err;
     }
 
-    if (!(s->text = av_realloc(s->text, textbuf_size + 1)))
+    if (!(tmp = av_realloc(s->text, textbuf_size + 1))) {
+        av_file_unmap(textbuf, textbuf_size);
         return AVERROR(ENOMEM);
+    }
+    s->text = tmp;
     memcpy(s->text, textbuf, textbuf_size);
     s->text[textbuf_size] = 0;
     av_file_unmap(textbuf, textbuf_size);