Target Hint array check

[kellrott]

Trying to fix sifter, and got the error:

goroutine 25 [running]:
github.com/bmeg/jsonschemagraph/graph.GraphSchema.Generate({0x140002b2c00?, 0x14000414000?}, {0x14000596038, 0x4}, 0x1400062c120, 0x0, 0x1400088bef0)
	/Users/ellrott/go/pkg/mod/github.com/bmeg/jsonschemagraph@v0.0.3-0.20241219173929-eecb8489b8f4/graph/generate.go:96 +0xf88
github.com/bmeg/sifter/transform.(*graphBuildProcess).Process(0x1400001e750, 0x1400062c120)
	/Users/ellrott/workspaces/sifter/transform/graph_build.go:94 +0x9c
github.com/bmeg/flame.(*FlatMapNode[...]).start.func1()
	/Users/ellrott/go/pkg/mod/github.com/bmeg/flame@v0.0.0-20231228021014-450efb0021a6/flatmap.go:24 +0xd0
created by github.com/bmeg/flame.(*FlatMapNode[...]).start in goroutine 1
	/Users/ellrott/go/pkg/mod/github.com/bmeg/flame@v0.0.0-20231228021014-450efb0021a6/flatmap.go:21 +0x94

Looks like line 96 is

						regex_match := target.TargetHints.RegexMatch[0]

So I think the target hint in the schema file isn't correctly formatted, which causes the regex to miss, which isn't checked before the array is accessed.