patch 8.0.0451: some macros are in lower case

Problem:    Some macros are in lower case.
Solution:   Make a few more macros upper case. Avoid lower case macros use an
            argument twice.
diff --git a/src/gui_gtk.c b/src/gui_gtk.c
index c015d7e..d22a3ce 100644
--- a/src/gui_gtk.c
+++ b/src/gui_gtk.c
@@ -1522,7 +1522,7 @@
 	    else if (*p == DLG_HOTKEY_CHAR)
 		*p++ = '_';
 	    else
-		mb_ptr_adv(p);
+		MB_PTR_ADV(p);
 	}
 	array[count] = NULL; /* currently not relied upon, but doesn't hurt */
     }