fix: enforce path !empty check no matter file/dir allow states

[rflandau]

Describe your changes

This PR corrects didSelectFile()'s logical precendence. Currently, m.Path's nil check is included in the truth value of isDir && m.DirAllowed rather than being a separate truth value. This is due to Go considering logical AND to have a higher precedence than logical OR (source).

Related issue/discussion: N/A

Tests/Steps To Reproduce

You can recreate this issue without any Bubble Tea infrastructure. Here is a trivial example:

func main() {
	path := ""
	fmt.Printf("%v <-- Current\n", true || false && path != "")
	fmt.Printf("%v <-- After This PR\n", (true || false) && path != "")
}

Will result in:

$ go run main.go 
true <-- Current
false <-- After This PR

Checklist before requesting a review

• I have read CONTRIBUTING.md
• I have performed a self-review of my code