Fix panic in VTOrc

[GuptaManan100]

Description

A panic was seen in VTOrc with the following log -

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x58 pc=0xec5205]

goroutine 1444 [running]:
vitess.io/vitess/go/vt/orchestrator/logic.electNewPrimary({_, _}, {{{0xc00134cd70, 0xc}, 0xcea}, {{0xc00134ce80, 0xc}, 0xcea}, 0x2, {0x0, ...}, ...}, ...)
	vitess.io/vitess/go/vt/orchestrator/logic/topology_recovery.go:1778 +0x485
vitess.io/vitess/go/vt/orchestrator/logic.executeCheckAndRecoverFunction({{{0xc00134cd70, 0xc}, 0xcea}, {{0xc00134ce80, 0xc}, 0xcea}, 0x2, {0x0, 0x0, 0x0}, ...}, ...)
	vitess.io/vitess/go/vt/orchestrator/logic/topology_recovery.go:1395 +0xbbe
vitess.io/vitess/go/vt/orchestrator/logic.CheckAndRecover.func1()
	vitess.io/vitess/go/vt/orchestrator/logic/topology_recovery.go:1483 +0x5f
created by vitess.io/vitess/go/vt/orchestrator/logic.CheckAndRecover
	vitess.io/vitess/go/vt/orchestrator/logic/topology_recovery.go:1482 +0x470

On investigation it was found to occur because the *events.Reparent field returned was nil and the code does not check if the field is nil.

This PR fixes this panic by checking if ev is nil before using its fields.

This PR also increases the timeout of the default values of LockShardTimeoutSeconds and WaitReplicasTimeoutSeconds to 30 seconds each.

Related Issue(s)

Checklist

• "Backport me!" label has been added if this change should be backported
• Tests were added or are not required
• Documentation was added or is not required

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[deepthi]

The changes look good.
I'm just wondering if it is possible to write a test for this at all.
If that is too hard, can you confirm that this was verified via manual testing?

[GuptaManan100]

@deepthi Yes, when I found the problem, I jumped and fixed it without adding a reproducing test. I have fixed that now. There is a test which reproduces the panic (and fails on main), which passes after the changes!