Application crashes with panic when lacking permissions for repository in OCI registry

[shurshun]

The application experiences a panic and crashes when it doesn't have the necessary permissions to access a repository in the OCI registry.
However, the login to the registry occurs without any issues, as the role being used has the "ecr:GetAuthorizationToken" permission.

# hpkl login -l AWS -p $(aws ecr get-login-password) 123456789123.dkr.ecr.eu-central-1.amazonaws.com
# hpkl resolve
2024-07-17T16:55:50.759Z	info	Resolving	{"name": "core.oci", "as": {"uri":"package://123456789123.dkr.ecr.eu-central-1.amazonaws.com/pkl/test-core@1.0.3","checksums":null,"name":"core.oci","project_file_uri":""}, "proto": "oci"}
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x68 pc=0x24d19c1]

goroutine 1 [running]:
hpkl.io/hpkl/pkg/app.(*Resolver).Resolve(0xc0009daae0, 0xc0009db0e0)
	/home/runner/work/hpkl/hpkl/pkg/app/resolver.go:131 +0x481
hpkl.io/hpkl/cmd.Resolve(0xc00092f300)
	/home/runner/work/hpkl/hpkl/cmd/resolve.go:94 +0x65
hpkl.io/hpkl/cmd.NewResolveCmd.func1(0xc000759600?, {0x4e08100?, 0x4?, 0x2d03876?})
	/home/runner/work/hpkl/hpkl/cmd/resolve.go:35 +0x3d
github.com/spf13/cobra.(*Command).execute(0xc00074bb08, {0x4e08100, 0x0, 0x0})
	/home/runner/go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:983 +0xaca
github.com/spf13/cobra.(*Command).ExecuteC(0x4d81a40)
	/home/runner/go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:1115 +0x3ff
github.com/spf13/cobra.(*Command).Execute(...)
	/home/runner/go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:1039
hpkl.io/hpkl/cmd.Execute()
	/home/runner/work/hpkl/hpkl/cmd/root.go:34 +0x1a
main.main()
	/home/runner/work/hpkl/hpkl/main.go:9 +0xf