Pacify gcc -Og -Wuninitialized

Pacify gcc -Og -Wuninitialized

This addresses the -Og uninitialized variable warnings I ran
into on Fedora 28, which uses 8.1.1 20180712 (Red Hat 8.1.1-5).
It also changes some explicit initializations to UNINIT
when the variable does not actually need to be initialized.
* src/process.c (connect_network_socket):
* src/sysdep.c (system_process_attributes):
* src/xfns.c (x_real_pos_and_offsets):
* src/xterm.c (get_current_wm_state) [USE_XCB]:
Add UNINIT.
* src/editfns.c (tzlookup):
* src/fns.c (Fnconc):
* src/font.c (font_parse_fcname):
* src/frame.c (x_set_frame_parameters):
Prefer UNINIT to explicit initialization.