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)
diff --git a/src/version.c b/src/version.c
index c0a5845..29488c2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    537,
+/**/
     536,
 /**/
     535,