patch 9.0.1945: Vim9: missing support for ro-vars in interface

Problem:  Vim9: missing support for ro-vars in interface
Solution: Support only read-only object variables in an interface,
          add additional checks when parsing class definitions.

closes: #13183
cloess: #13184
cloess: #13185.
closes: #13188

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/src/eval.c b/src/eval.c
index eaca2f5..5edda68 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1220,8 +1220,7 @@
 	int r = OK;
 	if (v_type == VAR_LIST && lp->ll_tv->vval.v_list == NULL)
 	    r = rettv_list_alloc(lp->ll_tv);
-	else if (v_type == VAR_BLOB
-					     && lp->ll_tv->vval.v_blob == NULL)
+	else if (v_type == VAR_BLOB && lp->ll_tv->vval.v_blob == NULL)
 	    r = rettv_blob_alloc(lp->ll_tv);
 	if (r == FAIL)
 	    return NULL;