patch 8.1.0537: ui_breakcheck() may be called recursively

Problem:    ui_breakcheck() may be called recursively, which doesn't work.
Solution:   When called recursively, just return. (James McCoy, closes #3617)

src/version.c

@@ -792,6 +792,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    537,
 /**/
     536,
 /**/