patch 8.2.4534: Vim9: "is" operator with empty string and null returns true

Problem:    Vim9: "is" operator with empty string and null returns true.
Solution:   Consider empty string and null to be different for "is".

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4534,
 /**/
     4533,
 /**/