patch 9.0.1217: using an object member in a closure doesn't work

Problem:    Using an object member in a closure doesn't work.
Solution:   Initialize lv_loop_depth. (closes #11840)
diff --git a/src/vim9compile.c b/src/vim9compile.c
index c89c37a..3a55186 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -66,6 +66,7 @@
 	if (lvar != NULL)
 	{
 	    CLEAR_POINTER(lvar);
+	    lvar->lv_loop_depth = -1;
 	    lvar->lv_name = (char_u *)(is_super ? "super" : "this");
 	    if (cctx->ctx_ufunc->uf_class != NULL)
 	    {