patch 8.0.0448: some macros are in lower case

Problem:    Some macros are in lower case, which can be confusing.
Solution:   Make a few lower case macros upper case.
diff --git a/src/move.c b/src/move.c
index c4f21a7..3d6d2ec 100644
--- a/src/move.c
+++ b/src/move.c
@@ -210,7 +210,7 @@
     /*
      * If the buffer is empty, always set topline to 1.
      */
-    if (bufempty())		/* special case - file is empty */
+    if (BUFEMPTY())		/* special case - file is empty */
     {
 	if (curwin->w_topline != 1)
 	    redraw_later(NOT_VALID);