patch 8.2.2787: MS-Windows: crash when using :echoconsole

Problem:    MS-Windows: crash when using :echoconsole.
Solution:   Do not write a NUL when it's already there.

src/os_win32.c

@@ -6411,6 +6411,8 @@ mch_write(
 	return;
 # endif
 
+    // Avoid writing to a string literal.
+    if (s[len] != NUL)
 	s[len] = NUL;
 
     if (!term_console)
@@ -6433,7 +6435,7 @@ mch_write(
 	    return;
 	}
 
-	while((ch = s[++prefix]))
+	while ((ch = s[++prefix]))
 	    if (ch <= 0x1e && !(ch != '\n' && ch != '\r' && ch != '\b'
 						&& ch != '\a' && ch != '\033'))
 		break;

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2787,
 /**/
     2786,
 /**/