VTGate MoveTables Buffering: Fix panic when buffering is disabled

[rohit-nayak-ps]

Description

When buffering is turned off in vtgate there is a possibility of a panic when a query is retried, because of this code
timeout := e.resolver.scatterConn.gateway.buffer.GetConfig().MaxFailoverDuration / (MaxBufferingRetries - 1) introduced here: https://github.com/vitessio/vitess/pull/15701/files#diff-19aa815da9f21f65b55cc865090e2cefa77af98b30b134936853f7763898d255R107 in v20.0.

This PR uses the default timeout of 30 seconds, used earlier, if buffering is turned off.

Related Issue(s)

#16858

Checklist

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[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 69.42%. Comparing base (f40e076) to head (67ee014).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtgate/plan_execute.go	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16922      +/-   ##
==========================================
- Coverage   69.43%   69.42%   -0.02%     
==========================================
  Files        1570     1570              
  Lines      203812   203923     +111     
==========================================
+ Hits       141517   141571      +54     
- Misses      62295    62352      +57     

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[harshit-gangal]

Let's add a unit test for the change.

[mattlord]

LGTM! I was going to suggest the same thing though ^^ 🙂 If it's very difficult to do for some reason then we can put that off.

[rohit-nayak-ps]

@harshit-gangal, where would I do that now and what should the unit test check for? I don't see any obvious framework to add a test for newExecute and there is no plan_execute_test.go

[harshit-gangal]

It can be placed in executor_test.
Let me see if I can add it