Fix relativeDepth check

[tommcc]

Summary of changes:

• Fix syntax of depth check fallback in case of files at depth 0.

When parsing files at the 0th level (e.g., markdown associated with 1st-level folders), this regex returns undefined. The|| [] was meant to guard against checking .length of undefined, but was ineffective due to this missing a pair of parentheses.

Should I attempt to add a test for this, or is it simple enough to go in as-is?

[bmuenzenmeyer]

Interesting find, something that seems to have been overlooked for a long time. Sounds as if this would make patternType markdown processing easier, something I attempted but ultimately left hanging as #415.

I see this just getting a once over and merge - no need for a unit test