Fix panic in vttablet when closing topo server twice

[frouioui]

Description

As described in #17093 we were closing the topo server in vttablet twice: in a defer function, and right before returning an error. This PR fixes the issue.

Using the same reproduction as the one detailed in the issue, we get:

$  kubectl logs example-vttablet-zone1-2469782763-bfadd780
W1028 20:22:32.006847       1 log.go:39] Failed to read in config : Config File "vtconfig" Not Found in "[/]". This is optional, and can be ignored if you are not using config files. For a detailed explanation, see https://github.com/vitessio/vitess/blob/main/doc/viper/viper.md#config-files.
I1028 20:22:32.014869       1 servenv_unix.go:57] Version: 22.0.0-SNAPSHOT (Git revision 4550640e0882ad71d79bde47e78f7e2123522145 branch 'fix-double-close-of-topo-server-in-tablet') built on Mon Oct 28 19:58:23 UTC 2024 by vitess@buildkitsandbox using go1.23.2 linux/amd64
E1028 20:22:32.016878       1 syslogger.go:171] can't connect to syslog: Unix syslog delivery error
I1028 20:22:32.065152       1 streamlog.go:206] Streaming logs from TabletServer at /debug/querylog.
I1028 20:22:32.065451       1 streamlog.go:206] Streaming logs from TxLog at /debug/txlog.
I1028 20:22:32.080117       1 cli.go:205] Loaded config file  successfully:
consolidator: enable
consolidatorStreamQuerySize: 2097152
consolidatorStreamTotalSize: 134217728
...

As mentioned in the issue, this bug is present on release-21.0 and causes a crash (though it only happens if vttablet was not going to start anyway) so I am adding the Backport to: release-21.0 label to this PR.

Related Issue(s)

• Fixes Double Close() of the *topo.Server leads to panics when starting vttablet #17093

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

[vitess-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.44%. Comparing base (4550640) to head (14928e1).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17094      +/-   ##
==========================================
+ Coverage   67.15%   67.44%   +0.28%     
==========================================
  Files        1571     1571              
  Lines      252250   252249       -1     
==========================================
+ Hits       169409   170120     +711     
+ Misses      82841    82129     -712     

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[mattlord]

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