Initialize QgsPoint with the correct WkbType to store Z and M values

[tomasMizera]

Fixes #2910

In the following code:

QgsPoint point;
point.setX(1);
point.setY(2);
point.setZ(3);
point.setM(4);

Z and M values will be null. This happens on the version of QGIS that we use atm.
Not sure if this is a QGIS bug or feature though.
Needed to explicitly mention the WkbType.

Checked other places in the code, and they seem to be ok. Should be tested though if we record Z values atm

[PeterPetrik]

I think best to merge and test on master , this should be safe change anyways