#5 don't NPE on requests that arrive before init has completed

[toby cabot]

At least one JEE app server (Geronimo/Jetty) allows http requests before Maverick has finished its initialization which causes Maverick to throw an NPE:

java.lang.NullPointerException
at org.infohazard.maverick.Dispatcher.getCommand(Dispatcher.java:460)

Here's a tiny patch to initialize the "commands" Map with the EMPTY_MAP until the real map is ready.

[toby cabot]

patch to initialize /Dispatcher.commands with an empty map