context CHANGE be silent about NULL ctx in ly_ctx_destroy()

mimic free() behavior
diff --git a/src/context.c b/src/context.c
index 465db73..d49b237 100644
--- a/src/context.c
+++ b/src/context.c
@@ -267,7 +267,9 @@
 API void
 ly_ctx_destroy(struct ly_ctx *ctx, void (*private_destructor)(const struct lysc_node *node, void *priv))
 {
-    LY_CHECK_ARG_RET(ctx, ctx,);
+    if (!ctx) {
+        return;
+    }
 
     /* models list */
     for (; ctx->list.count; ctx->list.count--) {