fix(server): fix NPE causes server crash

[mattisonchao]

Motivation

Oct 16 17:43:07.322395 DBG Received list request component=leader-controller namespace=default request={"endExclusive":"__oxia/session/0000000000000000//","shard":"0","startInclusive":"__oxia/session/0000000000000000/"} shard=2 term=2
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x38 pc=0x1545b3b]

goroutine 1275 [running]:
github.com/streamnative/oxia/server.(*leaderController).list.func1()
	/home/runner/work/oxia/oxia/server/leader_controller.go:654 +0x25b
github.com/streamnative/oxia/common.DoWithLabels.func1({0x1b2cf80?, 0xc000833020?})
	/home/runner/work/oxia/oxia/common/pprof.go:46 +0x2f
runtime/pprof.Do({0x1b2cd50, 0x332be60}, {{0xc001294c00?, 0x1?, 0x1?}}, 0xc000880d10)
	/opt/hostedtoolcache/go/1.22.8/x64/src/runtime/pprof/runtime.go:51 +0x118
github.com/streamnative/oxia/common.DoWithLabels({0x1b2cd50, 0x332be60}, 0xc000880f40, 0xc000880dc8)
	/home/runner/work/oxia/oxia/common/pprof.go:42 +0x585
github.com/streamnative/oxia/server.(*leaderController).list(0xc000ef2120, {0x1b2cd50, 0x332be60}, 0xc001294b40, 0xc00073e540)
	/home/runner/work/oxia/oxia/server/leader_controller.go:639 +0x3b6
created by github.com/streamnative/oxia/server.(*leaderController).ListSliceNoMutex in goroutine 981
	/home/runner/work/oxia/oxia/server/leader_controller.go:686 +0x216
FAIL	github.com/streamnative/oxia/server	8.710s
ok  	github.com/streamnative/oxia/server/kv	8.788s	coverage: 80.2% of statements
ok  	github.com/streamnative/oxia/server/util	1.018s	coverage: 8.5% of statements
ok  	github.com/streamnative/oxia/server/wal	4.214s	coverage: 73.4% of statements
ok  	github.com/streamnative/oxia/server/wal/codec	1.014s	coverage: 83.8% of statements
ok  	github.com/streamnative/oxia/tests/security/auth	5.209s	coverage: 80.5% of statements
ok  	github.com/streamnative/oxia/tests/security/tls	10.355s	coverage: 32.7% of statements
FAIL
make: *** [Makefile:24: test] Error 1

https://github.com/streamnative/oxia/actions/runs/11370802586/attempts/2?pr=552

Modification

• Close resources before deleting.
• Add logic to avoid repeated closures