patch 8.2.1730: Vim9: cannot use member of unknown type

Problem:    Vim9: cannot use member of unknown type.
Solution:   When type is unknown us "any". (closes #6997)
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 52651f3..06ee2f5 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -5080,12 +5080,14 @@
 			}
 			else
 			{
-			    // An empty list or dict has a &t_void member,
+			    // An empty list or dict has a &t_unknown member,
 			    // for a variable that implies &t_any.
 			    if (stacktype == &t_list_empty)
 				lvar->lv_type = &t_list_any;
 			    else if (stacktype == &t_dict_empty)
 				lvar->lv_type = &t_dict_any;
+			    else if (stacktype == &t_unknown)
+				lvar->lv_type = &t_any;
 			    else
 				lvar->lv_type = stacktype;
 			}