maxId undefined when Inflating empty collection

Probably a rare use case, but I have encountered it.  When inflating a serialized db using loadJSON(), if a collection is empty it will attempt to copy data.maxId to store at collection level, but this is undefined. 
I am simply doing a test for 0 data length and setting to 0 if it is (empty).  Feel free to implement differently if you want.  Thanks for the library!
Merge pull request #4 from obeliskos/patch-2

maxId undefined when Inflating empty collection