fix(frozen): hiding multiple columns when using pinning gets out of sync

[ghiscoding]

No description provided.

[codecov]

Codecov Report

Merging #684 (223ab88) into master (b2b963c) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #684   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          157       157           
  Lines        10451     10453    +2     
  Branches      3669      3669           
=========================================
+ Hits         10451     10453    +2     

Impacted Files	Coverage Δ
...s/angular-slickgrid/extensions/extensionUtility.ts	100.00% <100.00%> (ø)
...ngular-slickgrid/extensions/headerMenuExtension.ts	100.00% <100.00%> (ø)

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