aStyles contains rtl::References, so the erase() call may cause "p" to
be deleted, while "p" is then used as a parameter to Broadcast;
avoid this by retaining the rtl::Reference on the stack a bit longer.
Valgrind warning observed in sc_unoapi sc.ScStyleFamilyObj on
libreoffice-3-6 branch, called by ScStyleFamilyObj::removeByName.

Change-Id: I96d6de85b1b182b5ae3f74e92987a7f137537ffb