strip colon, if present, from ACCOUNT value

[jesopo]

I noticed this after updating to a 2.9-dev build that prints ACCOUNT lines:

-- user has identified as :user

this pull request is a band-aid. the real solution here is to correctly tokenise IRC data as soon as it's read so :trailing parameters are just treated as another param in the argv array.

[codecov-commenter]

Codecov Report

Merging #1525 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1525   +/-   ##
=======================================
  Coverage   35.04%   35.04%           
=======================================
  Files         204      204           
  Lines       84374    84375    +1     
=======================================
+ Hits        29571    29572    +1     
  Misses      54803    54803           

Impacted Files	Coverage Δ
src/plugins/irc/irc-protocol.c	87.59% <100.00%> (+<0.01%)	⬆️

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[flashcode]

Hi,
Thanks for the PR, I fixed with a slightly different solution.