Fix css EOF duplicate errors

[BenSouchet]

Issue #4809 | Annotations: duplicate annotations in CSS mode

This Pull request fix a bug with the CSS Parser (file csslint.js), the bug is simple :
If a declaration is open { and after that the parser encounter the end of the file EOF it will throw twice a wrong error (Unexpected token 'null' at line 3, col 1.).

I imagine this edge case has never been considered, and therefore taken into account in the code.

Before / After

Before:

After:

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[codecov]

Codecov Report

Merging #4816 (1e4f9a2) into master (57ded09) will increase coverage by 0.03%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #4816      +/-   ##
==========================================
+ Coverage   71.12%   71.16%   +0.03%     
==========================================
  Files         554      554              
  Lines       55711    55715       +4     
  Branches    10419    10420       +1     
==========================================
+ Hits        39623    39648      +25     
+ Misses      16088    16067      -21     

Flag	Coverage Δ
unittests	71.16% <0.00%> (+0.03%)	⬆️

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

Impacted Files	Coverage Δ
lib/ace/mode/css/csslint.js	33.19% <0.00%> (-0.02%)	⬇️
lib/ace/mouse/default_gutter_handler.js	25.96% <0.00%> (-0.78%)	⬇️
lib/ace/layer/text.js	90.81% <0.00%> (-0.30%)	⬇️
lib/ace/tooltip.js	43.75% <0.00%> (+0.27%)	⬆️
lib/ace/editor.js	81.63% <0.00%> (+1.90%)	⬆️

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[BenSouchet]

By the way there is lot of odd elements in the csslint.js file, like these empty else statement:

ace/lib/ace/mode/css/csslint.js

Line 4902 in 3f93451

} else

ace/lib/ace/mode/css/csslint.js

Line 4910 in 3f93451

} else

If I had motivation and time I would try to fix a bit the file, but currently I will focus on fixing bugs I encounter.

[andrewnester]

I've only realised that this change is made in csslint code which is a 3rd party library. Ideally we would rather update the library and maybe the fix is there but the library is not maintained anymore. I'll take a closer look at the change and will leave my comments