seat/pointer: Initialize low_res_value

Fixes

    In file included from /usr/include/wayland-server-core.h:32,
                     from ../types/seat/wlr_seat_pointer.c:6:
    In function 'wl_fixed_from_double',
        inlined from 'wlr_seat_pointer_send_axis' at ../types/seat/wlr_seat_pointer.c:367:6:
    /usr/include/wayland-util.h:641:17: error: 'low_res_value' may be used uninitialized [-Werror=maybe-uninitialized]
      641 |         u.d = d + (3LL << (51 - 8));
          |               ~~^~~~~~~~~~~~~~~~~~~
    ../types/seat/wlr_seat_pointer.c: In function 'wlr_seat_pointer_send_axis':
    ../types/seat/wlr_seat_pointer.c:329:16: note: 'low_res_value' was declared here
      329 |         double low_res_value;
          |                ^~~~~~~~~~~~~

types/seat/wlr_seat_pointer.c

@@ -326,7 +326,7 @@ void wlr_seat_pointer_send_axis(struct wlr_seat *wlr_seat, uint32_t time,
 		send_source = true;
 	}
 
-	double low_res_value;
+	double low_res_value = 0.0;
 	int32_t low_res_value_discrete = 0;
 	update_value120_accumulators(client, orientation, value, value_discrete,
 		&low_res_value, &low_res_value_discrete);