terminal: Silence maybe-uninitialized warning

clients/terminal.c: In function 'redraw_handler':
clients/terminal.c:213:28: warning: 'machine.unicode' may be used
uninitialized in this function [-Wmaybe-uninitialized]
  struct utf8_state_machine machine;
                            ^~~~~~~

clients/terminal.c: In function 'handle_char':
clients/terminal.c:213:28: warning: 'machine.unicode' may be used
uninitialized in this function [-Wmaybe-uninitialized]

Warning produced by GCC 5.3 and 6.1, with -O3.

'I found it weird that the compiler wouldn’t see that, so I re-checked
the code.

I think with -O3, this specific "for" is compile-time unlooped, and
utf8_next_char inlined.  And there is *one* path that can keep
machine.state to utf8state_start, thus triggering the warning.

Without -O3, the function is globally tagged as “changing unicode”, so
no warning is produced.

[...]

Side note: I picked 0 as the default value, but maybe in this case
0xfffd would be better?'

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Acked-by: Emil Velikov <emil.l.velikov@gmail.com>

clients/terminal.c

@@ -124,6 +124,7 @@ init_state_machine(struct utf8_state_machine *machine)
 	machine->state = utf8state_start;
 	machine->len = 0;
 	machine->s.ch = 0;
+	machine->unicode = 0;
 }
 
 static enum utf8_state