libavformat/aviobuf: keep track of the original buffer-size and restore it after probe/ensure-seekback

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

libavformat/avio.h

@@ -146,6 +146,13 @@ typedef struct AVIOContext {
      * This field is internal to libavformat and access from outside is not allowed.
      */
     int writeout_count;
+
+    /**
+     * Original buffer size
+     * used internally after probing and ensure seekback to reset the buffer size
+     * This field is internal to libavformat and access from outside is not allowed.
+     */
+    int orig_buffer_size;
 } AVIOContext;
 
 /* unbuffered I/O */