UIServerModule: fix uninitialized m_server
UIServerModule: fix uninitialized m_server

Fixes: 1a275e5977d0 ("ui_server: start up by DependencyInjector")
Signed-off-by: Jan Viktorin <3eab6ac54c005c4408f608556a6663b7f2abede7@fit.vutbr.cz>

BeeeOn/server,BeeeOn/server,BeeeOn/server,BeeeOn/server