I investigated this a bit further and have a patch that fixes the right-arrow test file for me, I can open it and the arrow displays without problems.
Note that this is my very first foray into the Emacs source as well as into Objective-C.
The problem is that ns_findfonts is being passed an empty font_spec. (Why, I have no idea.) This crashes "[fdesc matchingFontDescriptorsWithMandatoryKeys: fkeys]". The fix is to check for this case and, if there are no keys in the font_spec, simply initialize matchingDescs to an empty array.