Cannot report an error about spelling inconsistencies of kind names

[nihei9]

When kind names contain spelling inconsistencies, maleeni v0.6.0 panics.

I made the following file:

{
	"name": "test",
	"entries": [
		{
			"kind": "foo_1",
			"pattern": "foo_1"
		},
		{
			"kind": "foo1",
			"pattern": "foo1"
		}
	]
}

Then I got the following error:

$ maleeni compile test.json
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x5262bb]

goroutine 1 [running]:
github.com/nihei9/maleeni/spec.findSpellingInconsistenciesErrors(0xc0001b83c0, 0x3, 0x4, 0x0, 0x3, 0xc0001b83c0, 0x2)
        /home/nihei9/src/github.com/nihei9/maleeni/spec/spec.go:259 +0xdb
github.com/nihei9/maleeni/spec.(*LexSpec).Validate(0xc0001830e0, 0x0, 0x200)
        /home/nihei9/src/github.com/nihei9/maleeni/spec/spec.go:225 +0xb28
github.com/nihei9/maleeni/compiler.Compile(0xc0001830e0, 0xc000217d18, 0x1, 0x1, 0x0, 0xc000226100, 0xc000217d10, 0xc000217d38, 0xc000217d38, 0x5cd045)
        /home/nihei9/src/github.com/nihei9/maleeni/compiler/compiler.go:37 +0x45
main.runCompile(0xc0001bef00, 0xc000183050, 0x1, 0x3, 0x0, 0x0)
        /home/nihei9/src/github.com/nihei9/maleeni/cmd/maleeni/compile.go:49 +0xe5
github.com/spf13/cobra.(*Command).execute(0xc0001bef00, 0xc000183020, 0x3, 0x3, 0xc0001bef00, 0xc000183020)
        /home/nihei9/go/pkg/mod/github.com/spf13/cobra@v1.1.3/command.go:852 +0x472
github.com/spf13/cobra.(*Command).ExecuteC(0x800100, 0x4626e0, 0xc0000526ef, 0xc000028800)
        /home/nihei9/go/pkg/mod/github.com/spf13/cobra@v1.1.3/command.go:960 +0x375
github.com/spf13/cobra.(*Command).Execute(...)
        /home/nihei9/go/pkg/mod/github.com/spf13/cobra@v1.1.3/command.go:897
main.Execute(0x7e9d88, 0xc00010e058)
        /home/nihei9/src/github.com/nihei9/maleeni/cmd/maleeni/root.go:22 +0x31
main.main()
        /home/nihei9/src/github.com/nihei9/maleeni/cmd/maleeni/main.go:8 +0x25

The expectation is that maleeni compile command prints an error message without panic.

[nihei9]

The commit fe865a8 has caused this bug.

hook variable passed to findSpellingInconsistenciesErrors function can be nil, so the function must check whether the variable is nil or not before using it.