mem: Make av_strdup allocate using av_realloc

This makes sure that pointers from av_strdup are reallocable,
which is used in av_dict_set if the AV_DICT_APPEND flag is set.

Nothing should rely on pointers from av_strdup being aligned.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavutil/mem.c

@@ -214,7 +214,7 @@ char *av_strdup(const char *s)
     char *ptr = NULL;
     if (s) {
         int len = strlen(s) + 1;
-        ptr = av_malloc(len);
+        ptr = av_realloc(NULL, len);
         if (ptr)
             memcpy(ptr, s, len);
     }