In retry_transfer_wrapper, do not check url_interrupt_cb, causes problems

when writing and pressing q during encoding. Instead, check url_interrupt_cb
at the end.

Note that when a protocol is interrupted by url_interrupt_cb, some data may
be silently discarded: the protocol context is not suitable for anything
anymore.

Signed-off-by: Nicolas George <nicolas.george@normalesup.org>
Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>
(cherry picked from commit 688c22e033)

libavformat/avio.c

@@ -237,6 +237,8 @@ static inline int retry_transfer_wrapper(URLContext *h, unsigned char *buf, int
         if (ret)
            fast_retries = FFMAX(fast_retries, 2);
         len += ret;
+        if (url_interrupt_cb())
+            return AVERROR(EINTR);
     }
     return len;
 }