patch 8.1.1753: use of popup window mask is inefficient

Problem:    Use of popup window mask is inefficient.
Solution:   Precompute and cache the mask.
diff --git a/src/version.c b/src/version.c
index 25bfd16..64f6a9e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1753,
+/**/
     1752,
 /**/
     1751,