applehttp: Fix the key check in handle_variant_args

The key string is supposed to contain the equals character,
too.  Since the checked string was wrong, and the return value
check was wrong too, it incorrectly seemed to work right before.

Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit 2b0decf60b)

libavformat/applehttp.c

@@ -181,7 +181,7 @@ struct variant_info {
 static void handle_variant_args(struct variant_info *info, const char *key,
                                 int key_len, char **dest, int *dest_len)
 {
-    if (strncmp(key, "BANDWIDTH", key_len)) {
+    if (!strncmp(key, "BANDWIDTH=", key_len)) {
         *dest     =        info->bandwidth;
         *dest_len = sizeof(info->bandwidth);
     }