patch 9.0.1240: cannot access a private object member in a lambda

Problem:    Cannot access a private object member in a lambda defined inside
            the class.
Solution:   Go up the context stack to find the class. (closes #11866)
diff --git a/src/vim9class.c b/src/vim9class.c
index 0262e02..4845005 100644
--- a/src/vim9class.c
+++ b/src/vim9class.c
@@ -1388,6 +1388,19 @@
 }
 
 /*
+ * Return TRUE if current context "cctx_arg" is inside class "cl".
+ * Return FALSE if not.
+ */
+    int
+inside_class(cctx_T *cctx_arg, class_T *cl)
+{
+    for (cctx_T *cctx = cctx_arg; cctx != NULL; cctx = cctx->ctx_outer)
+	if (cctx->ctx_ufunc != NULL && cctx->ctx_ufunc->uf_class == cl)
+	    return TRUE;
+    return FALSE;
+}
+
+/*
  * Make a copy of an object.
  */
     void