patch 8.2.5161: might still access invalid memory

Problem:    Might still access invalid memory.
Solution:   Add extra check for negative value.

Author: brammool

src/message.c

@@ -949,8 +949,10 @@ msg_may_trunc(int force, char_u *s)
     int		n;
     int		room;
 
+    // If something unexpected happened "room" may be negative, check for that
+    // just in case.
     room = (int)(Rows - cmdline_row - 1) * Columns + sc_col - 1;
-    if ((force || (shortmess(SHM_TRUNC) && !exmode_active))
+    if (room > 0 && (force || (shortmess(SHM_TRUNC) && !exmode_active))
 	    && (n = (int)STRLEN(s) - room) > 0)
     {
 	if (has_mbyte)

src/version.c

@@ -735,6 +735,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    5161,
 /**/
     5160,
 /**/