integration: don't panic if some file download is not complete

[AskAlexSharov]

now:

panic: compressed file "v1-000970-000980-beaconblocks.seg" dictionary is corrupted: size 191.7 MB but no words in it, fileName: v1-000970-000980-beaconblocks.seg

goroutine 1 [running]:
github.com/erigontech/erigon/cmd/integration/commands.allSnapshots.func1()
	/home/ubuntu/erigon/cmd/integration/commands/stages.go:1383 +0x9cb
sync.(*Once).doSlow(0x4000?, 0xc00143f6d0?)
	/home/ubuntu/go/pkg/mod/golang.org/[email protected]/src/sync/once.go:74 +0xc2
sync.(*Once).Do(...)
	/home/ubuntu/go/pkg/mod/golang.org/[email protected]/src/sync/once.go:65
github.com/erigontech/erigon/cmd/integration/commands.allSnapshots({0x2138fd0?, 0x3113860?}, {0x2141500?, 0xc001307440?}, {0x2144c88?, 0xc00084c1a0?})
	/home/ubuntu/erigon/cmd/integration/commands/stages.go:1327 +0x90
github.com/erigontech/erigon/cmd/integration/commands.openDB({{0x2144c88, 0xc001487420}, 0xc0012f4d20, 0x1f12f00, {0xc00092d7b8, 0x16}, 0x0, 0x20000000000, 0x40000000, 0xffffffffffffffff, ...}, ...)
	/home/ubuntu/erigon/cmd/integration/commands/root.go:112 +0x3b9
github.com/erigontech/erigon/cmd/integration/commands.init.func11(0x2f18ec0, {0x1c6f10c?, 0x4?, 0x1c6ef58?})
	/home/ubuntu/erigon/cmd/integration/commands/stages.go:305 +0x10a
github.com/spf13/cobra.(*Command).execute(0x2f18ec0, {0xc0014872c0, 0x2, 0x2})
	/home/ubuntu/go/pkg/mod/github.com/spf13/[email protected]/command.go:989 +0xab1
github.com/spf13/cobra.(*Command).ExecuteC(0x2f18340)
	/home/ubuntu/go/pkg/mod/github.com/spf13/[email protected]/command.go:1117 +0x3ff
github.com/spf13/cobra.(*Command).Execute(...)
	/home/ubuntu/go/pkg/mod/github.com/spf13/[email protected]/command.go:1041
github.com/spf13/cobra.(*Command).ExecuteContext(0x0?, {0x21390f0?, 0xc0012f4cd0?})
	/home/ubuntu/go/pkg/mod/github.com/spf13/[email protected]/command.go:1034 +0x47
main.main()
	/home/ubuntu/erigon/cmd/integration/main.go:34 +0xe6
exit status 2

integration print_stages must be reliable tool to understand state of Erigon node - even if node is broken or in weird state.