Screen flashes because `indexer` is not set in external nodes

[Keith-CY]

Describe the bug
I received a case that

1. Neuron's screen keeps flashing, the UI crashes and restarts;
2. Unhandled Rejection in task: Reason: Error: {"code":-32601,"message":"Method not found"} repeats in the Log

That means the external node is not started with indexer

Expected behavior
Message about the indexer(https://github.com/nervosnetwork/neuron/blob/7f3bc4802284529f62d50b0ca73b6e2046264c4a/packages/neuron-ui/src/locales/zh.json#L30) should display and the screen should not flash.

Additional
Neuron Version: v0.121.1
Platform: MacOS

[devchenyan]

nervosnetwork/neuron#3332