Adding call to pbook additional init function

[rbarrue]

As discussed in https://github.com/dguest/pandamonium/issues/70#issuecomment-2163345574, for panda-client versions < 1.5.48, the check for proxy and extraction of username was done when you created a PBookCore object (from the initializer). Now they default the username to None and to get it we have to call the init() function.

I tested this on top of master with command panda-kill-taskid 39770381 (old done task that I had) and it worked (complained that you can't kill tasks in done state but that's beside the point).