x/upgrade cmd for querying upgrade plan panics when no plan exists

[clevinson]

Steps to reproduce:

start & run a new chain, then:

 simd q upgrade plan

Results in the following error:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x5294214]

goroutine 1 [running]:
github.com/cosmos/cosmos-sdk/x/upgrade/client/cli.GetCurrentPlanCmd.func1(0xc001086580, 0x65b0cc8, 0x0, 0x0, 0x0, 0x0)
	/Users/cory/Code/cosmos/cosmos-sdk/x/upgrade/client/cli/query.go:50 +0x254
github.com/spf13/cobra.(*Command).execute(0xc001086580, 0x65b0cc8, 0x0, 0x0, 0xc001086580, 0x65b0cc8)
	/Users/cory/go/pkg/mod/github.com/spf13/cobra@v1.0.0/command.go:842 +0x47c
github.com/spf13/cobra.(*Command).ExecuteC(0xc000fa2840, 0x0, 0x0, 0xc001007f60)
	/Users/cory/go/pkg/mod/github.com/spf13/cobra@v1.0.0/command.go:950 +0x375
github.com/spf13/cobra.(*Command).Execute(...)
	/Users/cory/go/pkg/mod/github.com/spf13/cobra@v1.0.0/command.go:887
github.com/spf13/cobra.(*Command).ExecuteContext(...)
	/Users/cory/go/pkg/mod/github.com/spf13/cobra@v1.0.0/command.go:880
github.com/cosmos/cosmos-sdk/simapp/simd/cmd.Execute(0xc000fa2840, 0x5a6d8e0, 0xc001018e50)
	/Users/cory/Code/cosmos/cosmos-sdk/simapp/simd/cmd/root.go:82 +0x158
main.main()
	/Users/cory/Code/cosmos/cosmos-sdk/simapp/simd/main.go:11 +0x2a

[sahith-narahari]

fixed in #8280