Sketcher: Fix Polygon disappearing on creation with autoconstraints on

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Fixes #3154

About the fix:
- If a non-zero vector is passed to seekAutoConstraint, it will suggest a vertical/horizontal constraint, which does not
make sense in the construction method.
- Passing a zero vector enables to treat it like a point, so for example point on object will be suggested, but not vertical/horizontal constraints.

src/Mod/Sketcher/Gui/CommandCreateGeo.cpp

@@ -7182,7 +7182,7 @@ public:
             setPositionText(onSketchPos, text);
 
             sketchgui->drawEdit(EditCurve);
-            if (seekAutoConstraint(sugConstr2, onSketchPos, dV)) {
+            if (seekAutoConstraint(sugConstr2, onSketchPos, Base::Vector2d(0.f,0.f))) {
                 renderSuggestConstraintsCursor(sugConstr2);
                 return;
             }