Prevent panic nil map

[emosbaugh]

What this PR does / why we need it:

Fixed an issue where KOTS would crash if a Helm Chart is included with optional values and no values.

Starting Admin Console API on port 3000...

  • Listing releases

  • Pulling upstream
  • Creating base
panic: assignment to entry in nil map

goroutine 10595 [running]:
github.com/replicatedhq/kots/pkg/base.renderReplicatedHelmChart(0xc000f10000, {0xc001358a00?, 0xc000e2f000?, 0xc00039ef00?}, 0xc0011eeff0, 0x0?)
	/home/runner/work/kots/kots/pkg/base/replicated.go:218 +0xfac
github.com/replicatedhq/kots/pkg/base.renderReplicated(0xc000b460c0, 0xc0011eeff0)
	/home/runner/work/kots/kots/pkg/base/replicated.go:136 +0x631
github.com/replicatedhq/kots/pkg/base.RenderUpstream(0x53e4860?, 0xc00035a720?)
	/home/runner/work/kots/kots/pkg/base/render.go:37 +0x6c
github.com/replicatedhq/kots/pkg/pull.Pull({_, _}, {{0x0, 0x0}, {0xc000be6eb8, 0x15}, {0xc00005802e, 0x11}, {0xc000d348f0, 0x1, ...}, ...})
	/home/runner/work/kots/kots/pkg/pull/pull.go:340 +0x19cb
github.com/replicatedhq/kots/pkg/kotsadmupstream.DownloadUpdate({0xc00160c960, 0x1b}, {{0xc000d18ea0, 0x1b}, {0xc00124a058, 0x4}, {0xc001300250, 0x3}, {0xc001300228, 0x8}, ...}, ...)
	/home/runner/work/kots/kots/pkg/kotsadmupstream/upstream.go:226 +0x14b8
github.com/replicatedhq/kots/pkg/updatechecker.processUpdates({{0xc0012186c0, 0x1b}, 0x0, {0x0, 0x0}, 0x0, 0x0, 0x0, 0x0, 0x0}, ...)
	/home/runner/work/kots/kots/pkg/updatechecker/updatechecker.go:317 +0x1de
github.com/replicatedhq/kots/pkg/updatechecker.CheckForUpdates.func1()
	/home/runner/work/kots/kots/pkg/updatechecker/updatechecker.go:306 +0x8e
created by github.com/replicatedhq/kots/pkg/updatechecker.CheckForUpdates
	/home/runner/work/kots/kots/pkg/updatechecker/updatechecker.go:305 +0xd31

Which issue(s) this PR fixes:

Fixes NONE

Special notes for your reviewer:

Steps to reproduce

Does this PR introduce a user-facing change?

Fixed an issue where KOTS would crash if a Helm Chart is included with optional values and no values.

Does this PR require documentation?

NONE