patch 9.0.0502: a closure in a nested loop in a :def function does not work

Problem:    A closure in a nested loop in a :def function does not work.
Solution:   Use an array of loopvars, one per loop level.

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    502,
 /**/
     501,
 /**/