commons: fix server ids handling in map

[elinorbgr]

Client ids start at 1 and server ids start at SERVER_ID_LIMIT, not
SERVER_ID_LIMIT+1.

cc #224

[codecov]

Codecov Report

Merging #225 into master will decrease coverage by 21.84%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##           master     #225       +/-   ##
===========================================
- Coverage   73.38%   51.53%   -21.85%     
===========================================
  Files          49       49               
  Lines        3505     3419       -86     
===========================================
- Hits         2572     1762      -810     
- Misses        933     1657      +724

Flag	Coverage Δ
#native_lib	51.53% <0%> (+0.3%)	⬆️
#rust_impl	?

Impacted Files	Coverage Δ
wayland-commons/src/map.rs	7.14% <0%> (-75.76%)	⬇️
wayland-server/src/rust_imp/globals.rs	0% <0%> (-79.55%)	⬇️
wayland-server/src/rust_imp/resources.rs	0% <0%> (-76.32%)	⬇️
wayland-server/src/rust_imp/clients.rs	0% <0%> (-74.56%)	⬇️
wayland-server/src/rust_imp/display.rs	0% <0%> (-74.55%)	⬇️
wayland-client/src/rust_imp/display.rs	0% <0%> (-72.35%)	⬇️
wayland-server/src/rust_imp/mod.rs	0% <0%> (-70%)	⬇️
wayland-client/src/rust_imp/proxy.rs	0% <0%> (-69.35%)	⬇️
wayland-server/src/rust_imp/event_loop_glue.rs	0% <0%> (-66.67%)	⬇️
wayland-client/src/rust_imp/queues.rs	0% <0%> (-63.27%)	⬇️
... and 10 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d192197...bc7d804. Read the comment docs.

[elinorbgr]

The coverage issue is linked to xd009642/tarpaulin#190, I'll ignore it.