fix panic when Package returns nil

[SVilgelm]

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x8 pc=0x1010fe448]

goroutine 41605 [running]:
github.com/ykadowak/zerologlint.isInLogPkg(0x101404088?)
        /Users/sergeyvilgelm/Library/Mobile Documents/com~apple~CloudDocs/projects/sv-tools/gochecker/vendor/github.com/ykadowak/zerologlint/zerologlint.go:87 +0x68
github.com/ykadowak/zerologlint.run(0x140af2c1860)
        /Users/sergeyvilgelm/Library/Mobile Documents/com~apple~CloudDocs/projects/sv-tools/gochecker/vendor/github.com/ykadowak/zerologlint/zerologlint.go:41 +0x1d0
golang.org/x/tools/go/analysis/internal/checker.(*action).execOnce(0x1400f649900)
        /Users/sergeyvilgelm/Library/Mobile Documents/com~apple~CloudDocs/projects/sv-tools/gochecker/vendor/golang.org/x/tools/go/analysis/internal/checker/checker.go:762 +0x88c
sync.(*Once).doSlow(0x140038da798?, 0x100e6fec8?)
        /Users/sergeyvilgelm/go/go1.20.1/src/sync/once.go:74 +0x100
sync.(*Once).Do(...)
        /Users/sergeyvilgelm/go/go1.20.1/src/sync/once.go:65
golang.org/x/tools/go/analysis/internal/checker.(*action).exec(0x140267aef00?)
        /Users/sergeyvilgelm/Library/Mobile Documents/com~apple~CloudDocs/projects/sv-tools/gochecker/vendor/golang.org/x/tools/go/analysis/internal/checker/checker.go:678 +0x40
golang.org/x/tools/go/analysis/internal/checker.execAll.func1(0x0?)
        /Users/sergeyvilgelm/Library/Mobile Documents/com~apple~CloudDocs/projects/sv-tools/gochecker/vendor/golang.org/x/tools/go/analysis/internal/checker/checker.go:666 +0x24
created by golang.org/x/tools/go/analysis/internal/checker.execAll
        /Users/sergeyvilgelm/Library/Mobile Documents/com~apple~CloudDocs/projects/sv-tools/gochecker/vendor/golang.org/x/tools/go/analysis/internal/checker/checker.go:672 +0x154

[ykadowak]

Thanks for the catch!

If you happen to be an expert in this field, could you please tell me why this happens? I found this reproducible case like below but no idea why this returns nil on v.Package.

package a

import "golang.org/x/exp/slices"

func package_nil() {
	s := []int{1, 2, 3}
	slices.Sort(s)
}