Sorting a single column emits an 'onPage' event

[mkemmerling]

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Current behavior
In version 4.1.0 of the DataTable the setter for the first value triggers pagination which in turn emits an onPage event.

The sortSingle() method sets this.first = 0; which will therefore emit the onPage event.

Expected behavior
No onPage event emitted on sorting a single column.

That is, sortSingle() should probably set the private variable _first instead of first to 0 (as is done in all other places of the DataTable where the first value is reset).

Please tell us about your environment:*

• Angular version: 4.3.0

• PrimeNG version: 4.1.0

• Browser: all