Check the path is set before checking the file exists

[zeroSteiner]

This fixes an issue in the #load_metadata method where if @path_to_user_metadata was nil, the ::File.exists? check would crash. This was causing an issue on Pro when the Framework was being initialized and for whatever reason the user metadata path wasn't set. It probably makes sense to set the metadata, but given that there's a code path where it's not, we should only be using it when it is. This will at least make sure the framework can be initialized, albeit possibly slower without the cache.

Verification

• Start msfconsole
• See the framework loads