avformat/aviobuf: factorize buffer_size out

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

libavformat/aviobuf.c

@@ -201,12 +201,14 @@ int64_t avio_seek(AVIOContext *s, int64_t offset, int whence)
     int64_t offset1;
     int64_t pos;
     int force = whence & AVSEEK_FORCE;
+    int buffer_size;
     whence &= ~AVSEEK_FORCE;
 
     if(!s)
         return AVERROR(EINVAL);
 
-    pos = s->pos - (s->write_flag ? 0 : (s->buf_end - s->buffer));
+    buffer_size = s->buf_end - s->buffer;
+    pos = s->pos - (s->write_flag ? 0 : buffer_size);
 
     if (whence != SEEK_CUR && whence != SEEK_SET)
         return AVERROR(EINVAL);
@@ -219,7 +221,7 @@ int64_t avio_seek(AVIOContext *s, int64_t offset, int whence)
     }
     offset1 = offset - pos;
     if (!s->must_flush && (!s->direct || !s->seek) &&
-        offset1 >= 0 && offset1 <= (s->buf_end - s->buffer)) {
+        offset1 >= 0 && offset1 <= buffer_size) {
         /* can do the seek inside the buffer */
         s->buf_ptr = s->buffer + offset1;
     } else if ((!s->seekable ||