patch 8.1.1591: on error garbage collection may free memory in use

Problem:    On error garbage collection may free memory in use.
Solution:   Reset may_garbage_collect when evaluating expression mapping.
            Add tests. (Ozaki Kiichi, closes #4579)
diff --git a/src/version.c b/src/version.c
index 5db753c..c21c12c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1591,
+/**/
     1590,
 /**/
     1589,