Panic during TSO benchmark run.

[nolouch]

Bug Report

./bin/pd-tso-bench


[2024/07/26 15:57:19.682 +08:00] [INFO] [tso_dispatcher.go:241] ["[tso] tso stream is not ready"] [dc=global]
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x0 pc=0x104eb7b80]

goroutine 135 [running]:
time.(*Ticker).Stop(...)
	/opt/homebrew/Cellar/go/1.22.3/libexec/src/time/tick.go:45
main.reqWorker({0x1051de1d0, 0x14000630050}, {0x140000301b0, 0x1, 0x14000030ed0?}, 0x0, 0x14000430000)
	/Users/nolouch/program/go/pd/tools/pd-tso-bench/main.go:402 +0x300
created by main.bench in goroutine 1
	/Users/nolouch/program/go/pd/tools/pd-tso-bench/main.go:135 +0x630