fix(tray): check for visibility when docking

[anhnamtran]

What type of PR is this? (check all applicable)

• Refactor
• Feature
• Bug Fix
• Optimization
• Documentation Update
• Other: Replace this with a description of the type of this PR

Description

Fixes an issue where the tray docking logic does not account for the tray's visibility when docking new clients.

The fix is relatively simple as it just sets client->hidden to the tray's manager's before calling ensure_state.

Related Issues & Documents

Fixes #2968

Documentation (check all applicable)

• This PR requires changes to the Wiki documentation (describe the changes)
• This PR requires changes to the documentation inside the git repo (please add them to the PR).
• Does not require documentation changes

[patrick96]

LGTM! Thanks

[codecov]

Codecov Report

Merging #2973 (73188e5) into master (2cd0809) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2973      +/-   ##
==========================================
- Coverage   12.69%   12.69%   -0.01%     
==========================================
  Files         160      160              
  Lines       12530    12531       +1     
==========================================
  Hits         1591     1591              
- Misses      10939    10940       +1     

Flag	Coverage Δ
unittests	12.69% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/x11/tray_manager.cpp	0.00% <0.00%> (ø)