patch 8.2.2078: illegal memory access when using :print on invalid text

Problem:    Illegal memory access when using :print on invalid text. (Dhiraj
            Mishra)
Solution:   Check for more composing characters than supported. (closes #7399)
diff --git a/src/message.c b/src/message.c
index f8efabc..3f6d56e 100644
--- a/src/message.c
+++ b/src/message.c
@@ -1859,7 +1859,11 @@
 	else if (has_mbyte && (l = (*mb_ptr2len)(s)) > 1)
 	{
 	    col += (*mb_ptr2cells)(s);
-	    if (lcs_nbsp != NUL && list
+	    if (l >= MB_MAXBYTES)
+	    {
+		STRCPY(buf, "¿");
+	    }
+	    else if (lcs_nbsp != NUL && list
 		    && (mb_ptr2char(s) == 160
 			|| mb_ptr2char(s) == 0x202f))
 	    {