patch 9.0.2099: win32: terminal codes clear the terminal

Problem:  Terminal control codes¹ are sent even when silent
          mode is on, causing the terminal to clear up
Solution: Block any terminal codes when silent mode is on

¹https://learn.microsoft.com/en-us/windows/console/console-virtual-terminal-sequences

fixes: #12822
closes: #13521

Signed-off-by: Nir Lichtman <nir@lichtman.org>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/os_win32.c b/src/os_win32.c
index 92bc8c1..2bf0fe7 100644
--- a/src/os_win32.c
+++ b/src/os_win32.c
@@ -8578,6 +8578,9 @@
     DWORD   result;
     int	    len;
 
+    if (silent_mode)
+	return 0;
+
     va_start(list, format);
     len = vim_vsnprintf((char *)buf, 100, (char *)format, list);
     va_end(list);