avio: Fix sanity checks in ffurl_read*

This fixes e.g. reading data over HTTP, where the underlying
socket is set to read/write.
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavformat/avio.c

@@ -289,14 +289,14 @@ static inline int retry_transfer_wrapper(URLContext *h, unsigned char *buf, int
 
 int ffurl_read(URLContext *h, unsigned char *buf, int size)
 {
-    if (h->flags & AVIO_FLAG_WRITE)
+    if (!(h->flags & AVIO_FLAG_READ))
         return AVERROR(EIO);
     return retry_transfer_wrapper(h, buf, size, 1, h->prot->url_read);
 }
 
 int ffurl_read_complete(URLContext *h, unsigned char *buf, int size)
 {
-    if (h->flags & AVIO_FLAG_WRITE)
+    if (!(h->flags & AVIO_FLAG_READ))
         return AVERROR(EIO);
     return retry_transfer_wrapper(h, buf, size, size, h->prot->url_read);
 }