patch 8.0.0452: some macros are in lower case

Problem:    Some macros are in lower case.
Solution:   Make a few more macros upper case.
diff --git a/src/mbyte.c b/src/mbyte.c
index d9bca6b..7396a7c 100644
--- a/src/mbyte.c
+++ b/src/mbyte.c
@@ -886,7 +886,7 @@
 {
     if (MB_BYTE2LEN(p[0]) == 1)
     {
-	if (p[0] == NUL || vim_iswhite(p[0]))
+	if (p[0] == NUL || VIM_ISWHITE(p[0]))
 	    return 0;
 	if (vim_iswordc_buf(p[0], buf))
 	    return 2;