getBestRunMirror fails behind proxy

[AidanDelaney]

Summary

Often, when running behind a proxy, there are no accessible run images.

In previous pack releases this manifests as a failure to download the run image. In pack 0.33.2 this causes a panic.

$ pack build example --builder paketobuildpacks/builder-jammy-full --pull-policy never
panic: runtime error: index out of range [0] with length 0

goroutine 1 [running]:
github.com/buildpacks/pack/pkg/client.getBestRunMirror({0x101175cf0, 0xf}, {0x140004c5300, 0x36}, {0x101e6f1e0, 0x0, 0x102571460?}, {0x0?, 0x50?, 0x140001e6000?}, ...)
	github.com/buildpacks/pack/pkg/client/common.go:123 +0x2c0
github.com/buildpacks/pack/pkg/client.(*Client).resolveRunImage(0x140001fee70, {0x0?, 0x140004beb40?}, {0x101175cf0?, 0x1014e6700?}, {0x101175cf0?, 0x0?}, {{0x140004c5300, 0x36}, {0x101e6f1e0, ...}}, ...)
	github.com/buildpacks/pack/pkg/client/common.go:42 +0xb8
github.com/buildpacks/pack/pkg/client.(*Client).Build(_, {_, _}, {{0x0, 0x0}, {0x16f763783, 0x7}, {0x16f763795, 0x23}, {0x0, ...}, ...})
	github.com/buildpacks/pack/pkg/client/build.go:343 +0x604
github.com/buildpacks/pack/internal/commands.Build.func1(0x14000153200, {0x1400012c640?, 0x0?, 0x0?})
	github.com/buildpacks/pack/internal/commands/build.go:157 +0xd00
github.com/buildpacks/pack/internal/commands.Build.logError.func3(0x14000492700?, {0x1400012c640?, 0x4?, 0x1011685f1?})
	github.com/buildpacks/pack/internal/commands/commands.go:58 +0x48
github.com/spf13/cobra.(*Command).execute(0x14000153200, {0x1400012c5f0, 0x5, 0x5})
	github.com/spf13/cobra@v1.8.0/command.go:983 +0x840
github.com/spf13/cobra.(*Command).ExecuteC(0x14000152f00)
	github.com/spf13/cobra@v1.8.0/command.go:1115 +0x344
github.com/spf13/cobra.(*Command).Execute(...)
	github.com/spf13/cobra@v1.8.0/command.go:1039
github.com/spf13/cobra.(*Command).ExecuteContext(0x101617c78?, {0x10160fbe8?, 0x1400012c000?})
	github.com/spf13/cobra@v1.8.0/command.go:1032 +0x48
main.main()
	github.com/buildpacks/pack/cmd/pack/main.go:26 +0xd8

---

Reproduction

Steps

1. Run pack on a system with no Internet access
2. pack build example --builder paketobuildpacks/builder-jammy-full --pull-policy never
3. Note the above panic

Current behavior

It panics

Expected behavior

I would expect the previous behaviour where pack fails to access the run image

---

Environment

pack info

pack report
Pack:
  Version:  0.33.2+git-f2cffc4.build-5562
  OS/Arch:  darwin/arm64

Default Lifecycle Version:  0.18.5

Supported Platform APIs:  0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.10, 0.11, 0.12
Config:
  experimental: true

docker info

Not necessary here