patch 9.0.2001: Vim9: segfault with islocked()

Problem:  Vim9: segfault with islocked()
Solution: Check that the lval pointer is not null for objects and
          class variables

closes: #13295

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Ernie Rael <errael@raelity.com>
diff --git a/src/eval.c b/src/eval.c
index d9fbec2..93109ef 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1375,6 +1375,7 @@
 		      && v_type != VAR_OBJECT
 		      && v_type != VAR_CLASS)
 	{
+	    // TODO: have a message with obj/class, not just dict,
 	    if (!quiet)
 		semsg(_(e_dot_can_only_be_used_on_dictionary_str), name);
 	    return NULL;
@@ -1385,6 +1386,7 @@
 		&& v_type != VAR_OBJECT
 		&& v_type != VAR_CLASS)
 	{
+	    // TODO: have a message with obj/class, not just dict/list/blob,
 	    if (!quiet)
 		emsg(_(e_can_only_index_list_dictionary_or_blob));
 	    return NULL;
@@ -1739,10 +1741,6 @@
 		    }
 		}
 
-		// TODO: dont' check access if inside class
-		// TODO: is GLV_READ_ONLY the right thing to use
-		//	     for class/object member access?
-		//	     Probably in some cases. Need inside class check
 		if (lp->ll_valtype == NULL)
 		{
 		    int		m_idx;