patch 9.0.1138: crash when expecting varargs but it is something else

Problem:    Crash when expecting varargs but it is something else.
Solution:   Only use the member when the type is a list. (closes #11774)
diff --git a/src/vim9instr.c b/src/vim9instr.c
index bd2c1b4..72ecbaa 100644
--- a/src/vim9instr.c
+++ b/src/vim9instr.c
@@ -1841,7 +1841,13 @@
 		type_T	*expected;
 
 		if (varargs && i >= type->tt_argcount - 1)
-		    expected = type->tt_args[type->tt_argcount - 1]->tt_member;
+		{
+		    expected = type->tt_args[type->tt_argcount - 1];
+		    if (expected != NULL && expected->tt_type == VAR_LIST)
+			expected = expected->tt_member;
+		    if (expected == NULL)
+			expected = &t_any;
+		}
 		else if (i >= type->tt_min_argcount
 					     && actual->tt_type == VAR_SPECIAL)
 		    expected = &t_any;