Bug fix: Sketcher Polygon autoconstraints

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The autoconstraints on creation of an hexagon were not working.

How to reproduce?
1. In a sketch make a couple of lines
2. Create an hexagon (or other polygon of your choice) with center in one end of a line and with side coincident with the end point of the other line

Result:
Neither the center nor the side autoconstraints are properly created.

Fix:
Straightforward. Just correct the indexes. Last is always the circle. Last but one is always a side.

src/Mod/Sketcher/Gui/CommandCreateGeo.cpp

@@ -4512,15 +4512,15 @@ class DrawSketchHandlerRegularPolygon: public DrawSketchHandler
                 Gui::Command::commitCommand();
                 Gui::Command::updateActive();
 
-                // add auto constraints at the start of the first side
+                // add auto constraints at the center of the polygon
                 if (sugConstr1.size() > 0) {
-                    createAutoConstraints(sugConstr1, getHighestCurveIndex() - 3 , Sketcher::mid);
+                    createAutoConstraints(sugConstr1, getHighestCurveIndex(), Sketcher::mid);
                     sugConstr1.clear();
                 }
 
-                // add auto constraints at the end of the second side
+                // add auto constraints to the last side of the polygon
                 if (sugConstr2.size() > 0) {
-                    createAutoConstraints(sugConstr2, getHighestCurveIndex() - 2, Sketcher::end);
+                    createAutoConstraints(sugConstr2, getHighestCurveIndex() - 1, Sketcher::end);
                     sugConstr2.clear();
                 }
             }