Check if frs sync.Map is nil within handleArchive

[egibs]

@hectorj2f pointed out that we were still seeing nil pointer dereferences/panics when failing to scan archives (i.e., frs is nil):

[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x48955a]

goroutine 1652 [running]:
sync.(*Map).loadReadOnly(...)
	sync/map.go:114
sync.(*Map).Range(0x0?, 0x9a9154?)
	sync/map.go:478 +0x1a
github.com/chainguard-dev/malcontent/pkg/action.recursiveScan.func1({0xc00171fef0, 0x8d})
	github.com/chainguard-dev/malcontent/pkg/action/scan.go:246 +0x305
github.com/chainguard-dev/malcontent/pkg/action.recursiveScan.func3()
	github.com/chainguard-dev/malcontent/pkg/action/scan.go:292 +0x70
golang.org/x/sync/errgroup.(*Group).Go.func1()
	golang.org/x/sync@v0.8.0/errgroup/errgroup.go:78 +0x50
created by golang.org/x/sync/errgroup.(*Group).Go in goroutine 1
	golang.org/x/sync@v0.8.0/errgroup/errgroup.go:75 +0x96

This is the same issue as #462 but I only fixed the bug in the errIfHitOrMiss.

[hectorj2f]

Thanks @egibs