kvstore: Fix panic in `cilium kvstore` CLI
kvstore: Fix panic in `cilium kvstore` CLI

Fix the following panic when the kvstore client cannot be created via the CLI:

```
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x50 pc=0x1a306d0]

goroutine 1 [running]:
github.com/cilium/cilium/pkg/kvstore.Get(0x0, 0x0, 0x8, 0x8, 0x8, 0x7, 0x7)
	/home/vagrant/go/src/github.com/cilium/cilium/pkg/kvstore/kvstore.go:40 +0x40
github.com/cilium/cilium/cilium/cmd.glob..func32(0x44e3c80, 0x4ada920, 0x0, 0x0)
	/home/vagrant/go/src/github.com/cilium/cilium/cilium/cmd/kvstore_get.go:55 +0x2e7
github.com/cilium/cilium/vendor/github.com/spf13/cobra.(*Command).execute(0x44e3c80, 0x4ada920, 0x0, 0x0, 0x44e3c80, 0x4ada920)
	/home/vagrant/go/src/github.com/cilium/cilium/vendor/github.com/spf13/cobra/command.go:766 +0x2cc
github.com/cilium/cilium/vendor/github.com/spf13/cobra.(*Command).ExecuteC(0x44e7f00, 0x2f, 0xffffffffffffffff, 0xc0004c2f30)
	/home/vagrant/go/src/github.com/cilium/cilium/vendor/github.com/spf13/cobra/command.go:852 +0x2fd
github.com/cilium/cilium/vendor/github.com/spf13/cobra.(*Command).Execute(0x44e7f00, 0xc0007a7f58, 0x1164e30)
	/home/vagrant/go/src/github.com/cilium/cilium/vendor/github.com/spf13/cobra/command.go:800 +0x2b
github.com/cilium/cilium/cilium/cmd.Execute()
	/home/vagrant/go/src/github.com/cilium/cilium/cilium/cmd/root.go:46 +0x2d
main.main()
	/home/vagrant/go/src/github.com/cilium/cilium/daemon/main.go:32 +0xd0
```

Signed-off-by: Thomas Graf <5f50a84c1fa3bcff146405017f36aec1a10a9e38@cilium.io>

cilium/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,tgraf/cilium,cilium-team/cilium,tgraf/cilium,cilium/cilium,cilium-team/cilium,tklauser/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,tklauser/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,michi-covalent/cilium,michi-covalent/cilium