panic: Slice index out of range with / pattern in .gitignore files

[boyter]

If go-gitignore is supplied with a gitignore that consists of a single character / then it will panic with the following,

panic: runtime error: slice bounds out of range [:1] with length 0

this is due to the following code inside inital_holder.go

func (h *initialPatternHolder) add(pattern string) {
	trimedPattern := strings.TrimPrefix(pattern, "/")

	if strings.IndexAny(trimedPattern[0:1], initials) != -1 {
		h.patterns.set(trimedPattern[0], newPatternForEqualizedPath(pattern))
	} else {
		h.otherPatterns.add(newPatternForEqualizedPath(pattern))
	}
}

Where the trimmed pattern is changed from / to empty string and then trimedPattern[0:1] tries to reference outside the string length.

Not sure what the resolution for this is? Should it ignore the pattern? Return an error? I am not familiar enough with the semantics of .gitignore files to comment sorry.

Relates to boyter/scc#149