patch 8.1.2018: using freed memory when out of memory and displaying message

Problem:    Using freed memory when out of memory and displaying message.
Solution:   Make a copy of the message first.

src/main.c

@@ -1276,17 +1276,20 @@ main_loop(
 	    /* display message after redraw */
 	    if (keep_msg != NULL)
 	    {
-		char_u *p;
+		char_u *p = vim_strsave(keep_msg);
 
-		// msg_attr_keep() will set keep_msg to NULL, must free the
+		if (p != NULL)
-		// string here. Don't reset keep_msg, msg_attr_keep() uses it
+		{
-		// to check for duplicates.  Never put this message in history.
+		    // msg_start() will set keep_msg to NULL, make a copy
-		p = keep_msg;
+		    // first.  Don't reset keep_msg, msg_attr_keep() uses it to
+		    // check for duplicates.  Never put this message in
+		    // history.
 		    msg_hist_off = TRUE;
 		    msg_attr((char *)p, keep_msg_attr);
 		    msg_hist_off = FALSE;
 		    vim_free(p);
 		}
+	    }
 	    if (need_fileinfo)		/* show file info after redraw */
 	    {
 		fileinfo(FALSE, TRUE, FALSE);

src/message.c

@@ -168,11 +168,6 @@ msg_attr_keep(
 	ch_log(NULL, "ERROR: %s", (char *)s);
 #endif
 
-    /* When displaying keep_msg, don't let msg_start() free it, caller must do
-     * that. */
-    if ((char_u *)s == keep_msg)
-	keep_msg = NULL;
-
     /* Truncate the message if needed. */
     msg_start();
     buf = msg_strtrunc((char_u *)s, FALSE);

src/normal.c

@@ -1182,13 +1182,18 @@ getcount:
 
 	    kmsg = keep_msg;
 	    keep_msg = NULL;
-	    /* showmode() will clear keep_msg, but we want to use it anyway */
+	    // showmode() will clear keep_msg, but we want to use it anyway
 	    update_screen(0);
-	    /* now reset it, otherwise it's put in the history again */
+	    // now reset it, otherwise it's put in the history again
 	    keep_msg = kmsg;
+
+	    kmsg = vim_strsave(keep_msg);
+	    if (kmsg != NULL)
+	    {
 		msg_attr((char *)kmsg, keep_msg_attr);
 		vim_free(kmsg);
 	    }
+	}
 	setcursor();
 	cursor_on();
 	out_flush();

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2018,
 /**/
     2017,
 /**/