Fixes the following panic triggered by blob Hive tests:
[2c098836] panic: runtime error: index out of range [0] with length 0
[2c098836]
[2c098836] goroutine 902 [running]:
[2c098836] github.com/ledgerwatch/erigon-lib/txpool.MainLoop.func1()
[2c098836] github.com/ledgerwatch/erigon-lib@v0.0.0-20230801100033-1b342f37741d/txpool/pool.go:1565 +0x100f
[2c098836] created by github.com/ledgerwatch/erigon-lib/txpool.MainLoop
[2c098836] github.com/ledgerwatch/erigon-lib@v0.0.0-20230801100033-1b342f37741d/txpool/pool.go:1492 +0x8c5
Fixes the following panic triggered by blob Hive tests: