Only reset buffer state if seeking is successful; update seek reg ref.

Originally committed as revision 14491 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/aviobuf.c

@@ -163,14 +163,13 @@ offset_t url_fseek(ByteIOContext *s, offset_t offset, int whence)
         if (s->write_flag) {
             flush_buffer(s);
             s->must_flush = 1;
-        } else
-#endif /* defined(CONFIG_MUXERS) || defined(CONFIG_NETWORK) */
-        {
-            s->buf_end = s->buffer;
         }
-        s->buf_ptr = s->buffer;
+#endif /* defined(CONFIG_MUXERS) || defined(CONFIG_NETWORK) */
         if (!s->seek || (res = s->seek(s->opaque, offset, SEEK_SET)) < 0)
             return res;
+        if (!s->write_flag)
+            s->buf_end = s->buffer;
+        s->buf_ptr = s->buffer;
         s->pos = offset;
     }
     s->eof_reached = 0;