Segfault when no access on directory

[GeoffreyFrogeye]

Context

Specifiying a path in the input section where the user running grok_exporter doesn't have rights to open a folder in the path e.g. /var/log/software/software.log where the user don't have access to the software folder.

Actual behavior

It segfaults:

Starting server on http://machinename:9144/metrics
panic: runtime error: invalid memory address or nil pointer dereference
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x89f652]

goroutine 15 [running]:
github.com/fstab/grok_exporter/tailer/fswatcher.(*watcher).unwatchDir(0xc000195cb8, 0x0, 0x28, 0x8)
	/go/src/github.com/fstab/grok_exporter/tailer/fswatcher/fswatcher_linux.go:38 +0x42
github.com/fstab/grok_exporter/tailer/fswatcher.(*fileTailer).shutdown(0xc000241440)
	/go/src/github.com/fstab/grok_exporter/tailer/fswatcher/fswatcher.go:211 +0xbb
panic(0x96ab60, 0x108f0b0)
	/usr/local/go/src/runtime/panic.go:679 +0x1b2
github.com/fstab/grok_exporter/tailer/fswatcher.(*Dir).Path(...)
	/go/src/github.com/fstab/grok_exporter/tailer/fswatcher/file_linux.go:29
github.com/fstab/grok_exporter/tailer/fswatcher.runFileTailer.func1(0xc000241440, 0xadcce0, 0xc000259e30, 0xc0002567d0, 0x9e0001)
	/go/src/github.com/fstab/grok_exporter/tailer/fswatcher/fswatcher.go:146 +0x19f
created by github.com/fstab/grok_exporter/tailer/fswatcher.runFileTailer
	/go/src/github.com/fstab/grok_exporter/tailer/fswatcher/fswatcher.go:129 +0x212

Expected behaviour

Get an error in the lines of Permission denied

Info

From release : grok_exporter-1.0.0.RC3.linux-amd64.zip

OS: Debian 9

[fstab]

Thanks a lot for reporting. Fixed it.