patch 9.2.0150: synchronized terminal update may cause display artifacts

Problem:  When using synchronized terminal output, the internal
          output buffer  is not flushed before sending the
          End Synchronized Update (ESU) sequence. This causes
          redrawing artifacts.
Solution: Call out_flush() immediately before sending the ESU
          sequence to ensure all pending drawing commands are
          contained within the synchronized update window.
          (Yasuhiro Matsumoto)

closes: #19662

Signed-off-by: Yasuhiro Matsumoto <mattn.jp@gmail.com>
Signed-off-by: Foxe Chen <chen.foxe@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/term.c

@@ -8056,6 +8056,11 @@ term_set_sync_output(int flags)
     {
 	if (sync_output_state == 0 || --sync_output_state > 0)
 	    return;
+	// Flush the output buffer before ending the sync batch so that
+	// all drawing output is sent to the terminal within the
+	// BSU..ESU window.  Without this, the drawing data remaining in
+	// out_buf would be sent after ESU, outside the sync batch.
+	out_flush();
 	str = T_ESU;
     }
     else

src/version.c

@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    150,
 /**/
     149,
 /**/