patch 8.1.0641: no check for out-of-memory when converting regexp

Problem:    No check for out-of-memory when converting regexp.
Solution:   Bail out when lalloc() returns NULL. (John Marriott)

src/version.c

@@ -799,6 +799,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    641,
 /**/
     640,
 /**/