Only changes the ViewSystem if the user confirms

UnitsApi::setSchema() was being called when the user changed the
comboBox item, so the view system was saved if the user later clicked
Cancel.  This call was moved to the saveSettings() method that is called
only if the user clicks Apply or OK.

src/Gui/DlgSettingsUnitsImp.cpp

@@ -78,8 +78,6 @@ void DlgSettingsUnitsImp::on_comboBox_ViewSystem_currentIndexChanged(int index)
     if (index < 0)
         return; // happens when clearing the combo box in retranslateUi()
 
-    UnitsApi::setSchema((UnitSystem)index);
-
     // Enable/disable the fractional inch option depending on system
     if( (UnitSystem)index == ImperialBuilding )
     {
@@ -96,6 +94,7 @@ void DlgSettingsUnitsImp::saveSettings()
     // must be done as very first because we create a new instance of NavigatorStyle
     // where we set some attributes afterwards
     int FracInch;  // minimum fractional inch to display
+    int viewSystemIndex; // currently selected View System (unit system)
 
     ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath
         ("User parameter:BaseApp/Preferences/Units");
@@ -116,6 +115,10 @@ void DlgSettingsUnitsImp::saveSettings()
 
     // Set the actual format value
     Base::QuantityFormat::setDefaultDenominator(FracInch);
+
+    // Set and save the Unit System
+    viewSystemIndex = ui->comboBox_ViewSystem->currentIndex();
+    UnitsApi::setSchema((UnitSystem)viewSystemIndex);
 }
 
 void DlgSettingsUnitsImp::loadSettings()