[PD] fix division by zero in Helix

- when a helix is defined in the growth mode it can have a pitch of zero

This commit fixes the resulting division by zero by directly setting the known turns

src/Mod/PartDesign/Gui/TaskHelixParameters.cpp

@@ -475,7 +475,7 @@ void TaskHelixParameters::onModeChanged(int index)
 
     ui->pitch->setValue(propPitch->getValue());
     ui->height->setValue(propHeight->getValue());
-    ui->turns->setValue((propHeight->getValue()) / (propPitch->getValue()));
+    ui->turns->setValue(propTurns->getValue());
 
     recomputeFeature();
     updateUI();