patch 8.0.0287: debug mode: cannot access function arguments

Problem:    Cannot access the arguments of the current function in debug mode.
            (Luc Hermitte)
Solution:   use get_funccal(). (Lemonboy, closes #1432, closes #1352)

src/userfunc.c

@@ -3556,7 +3556,7 @@ get_funccal_args_var()
 {
     if (current_funccal == NULL)
 	return NULL;
-    return &current_funccal->l_avars_var;
+    return &get_funccal()->l_avars_var;
 }
 
 /*

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    287,
 /**/
     286,
 /**/