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.

src/gui.c

@@ -4500,7 +4500,7 @@ scroll_line_len(linenr_T lnum)
 	for (;;)
 	{
 	    w = chartabsize(p, col);
-	    mb_ptr_adv(p);
+	    MB_PTR_ADV(p);
 	    if (*p == NUL)		/* don't count the last character */
 		break;
 	    col += w;