Return error in podman system service if URI scheme is not unix/tcp

[boaz0]

If tcp or unix are missing from the URI podman panics:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x13fe9a1]

goroutine 1 [running]:
github.com/containers/podman/v4/pkg/api/server.newServer(0xc000296540, {0x0, 0x0}, {{0x0, 0x0}, {0x0, 0x0}, 0x0, {0x7ffca77de322, 0xe}})
	/home/b0/go/src/github.com/boaz0/podman/pkg/api/server/server.go:65 +0x41
github.com/containers/podman/v4/pkg/api/server.NewServerWithSettings(...)
	/home/b0/go/src/github.com/boaz0/podman/pkg/api/server/server.go:61
github.com/containers/podman/v4/cmd/podman/system.restService(0x7ffca77de322?, 0xe?, {{0x0, 0x0}, {0x0, 0x0}, 0x0, {0x7ffca77de322, 0xe}})
	/home/b0/go/src/github.com/boaz0/podman/cmd/podman/system/service_abi.go:115 +0x865
github.com/containers/podman/v4/cmd/podman/system.service(0x2410ee0?, {0xc0002c48a0?, 0x1?, 0x3?})
	/home/b0/go/src/github.com/boaz0/podman/cmd/podman/system/service.go:103 +0x26a
github.com/spf13/cobra.(*Command).execute(0x2410ee0, {0xc0001a6150, 0x3, 0x3})
	/home/b0/go/src/github.com/boaz0/podman/vendor/github.com/spf13/cobra/command.go:872 +0x694
github.com/spf13/cobra.(*Command).ExecuteC(0x2414fe0)
	/home/b0/go/src/github.com/boaz0/podman/vendor/github.com/spf13/cobra/command.go:990 +0x3bd
github.com/spf13/cobra.(*Command).Execute(...)
	/home/b0/go/src/github.com/boaz0/podman/vendor/github.com/spf13/cobra/command.go:918
github.com/spf13/cobra.(*Command).ExecuteContext(...)
	/home/b0/go/src/github.com/boaz0/podman/vendor/github.com/spf13/cobra/command.go:911
main.Execute()
	/home/b0/go/src/github.com/boaz0/podman/cmd/podman/root.go:105 +0xc5
main.main()
	/home/b0/go/src/github.com/boaz0/podman/cmd/podman/main.go:40 +0x7c

The reason for that is because if the schema is not unix or tcp the listener is nil and at server/server.go:65 listener.Addr() is being called but listener is nil

Does this PR introduce a user-facing change?

None

[edsantiago]

LGTM but I'm wondering how many (if any) cases there are where this has somehow been working, and will now error out.

[boaz0]

@edsantiago - that's what I thought too but I couldn't find any explanation/use-cases where other scheme/protocols are used. Would like to come up with a better solution, though.

[mheon]

Hm. I think this is OK, but someone more familiar with remote should take a look. @baude PTAL

[Luap99]

This never worked since the listener var would be nil in this case -> therefore no socket/server

[edsantiago]

Tests green, LGTM.

[Luap99]

/lgtm

[openshift-ci]

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