Fix sending a ServerLost error when reading a packet fails

[GuptaManan100]

Description

Once a connection has received a connection error from MySQL, we close the connection in dbconn and other callers. In order for this close to work properly we should be sending a MySQL.CRServerLost error.
All the callers of readEphemeralPacket wrap the error and send this error so that the connection can be closed. However, there is one code-path that doesn't do this.

We believe that is an issue. Not sending a mysql.CRServerLost error causes the connection to remain open and be reused for the rollback call, even though the connection isn't usable any more. This causes a panic in the code, since we didn't cleanup the state when we error out the first time.

This PR fixes the issue after adding a failing test which ensures that we receive a CRServerLost error on MySQL crashing after only sending a field packet.

Related Issue(s)

• Fixes Bug Report: Panic in Rollback of a transaction after MySQL crash #11921

Checklist

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Deployment Notes

[vitess-bot]

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