Fix determination of anonymous code blocks in Postgres Mode

[mkslanc]

Issue #, if available: #4790

Description of changes:
Highlight of anonymous code block now wouldn't break highlight of other tokens

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[codecov]

Codecov Report

Merging #4865 (a96adac) into master (649dd68) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4865   +/-   ##
=======================================
  Coverage   70.06%   70.06%           
=======================================
  Files         557      557           
  Lines       58220    58220           
  Branches    11195    11195           
=======================================
  Hits        40794    40794           
  Misses      17426    17426           

Flag	Coverage Δ
unittests	70.06% <ø> (ø)

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Impacted Files	Coverage Δ
lib/ace/mode/pgsql_highlight_rules.js	100.00% <ø> (ø)

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[andrewnester]

Thanks, merged!