localchans: recreate missing edge if not found

[JssDWt]

Change Description

Description of change / link to associated issue.If a node contains a channel, but doesn't have a corresponding edge in the graph database, updating the channel policy would fail. In this commit the edge is recreated if the channel exists. This ensures a node can recover from a missing edge in the graph database by calling updatechanpolicy.

Alternative for https://github.com/lightningnetwork/lnd/pull/8768, namely option 2 in https://github.com/lightningnetwork/lnd/pull/8768#issuecomment-2143799767 Partially fixes https://github.com/lightningnetwork/lnd/issues/7261 by allowing to recreate the edge by calling updatechanpolicy.

Steps to Test

• Create a node that has a channel with a missing edge
• Calling getchaninfo on this channel will fail
• Call updatechanpolicy on this channel
• Calling getchaninfo on this channel should succeed

I'm not sure how to create an integration test where I can modify the graph database to delete an edge in order to test this. Please advise.

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