[Build] Do not require dbus and dleyna-connector-dbus at build time

DBus and the DBus connector are only needed at runtime and dropping the
pkg-config checks in ./configure allows the build to succeed even in
restricted build environment with minimal dependecies.
[Server] Fix a crash case when the server stops

Signed-off-by: Regis Merlino <regis.merlino@intel.com>