Fixed parsing of conditionals in COUNTIF functions

Conditional operators in the selection parameter of COUNTIF
functions were not being parsed properly, causing evaluations
of formulae with such functions to sometimes fail.

Fixes PHPOffice#526
Closes PHPOffice#528

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Xlsx reader do not read rows and columns filtered out in readFilter at all - [#370](https://github.com/PHPOffice/PhpSpreadsheet/issues/370)
 - Make newer Excel versions properly recalculate formulas on document open - [#456](https://github.com/PHPOffice/PhpSpreadsheet/issues/456)
 - `Coordinate::extractAllCellReferencesInRange()` throws an exception for an invalid range – [#519](https://github.com/PHPOffice/PhpSpreadsheet/issues/519)
+- Fixed parsing of conditionals in COUNTIF functions - [#526](https://github.com/PHPOffice/PhpSpreadsheet/issues/526)
 
 ## [1.2.1] - 2018-04-10