[CURA-12061] Remove early-out: Restore 'side-effects' of unioning wit…

…h empty. (#2124)

src/geometry/Shape.cpp

@@ -181,14 +181,7 @@ Shape Shape::unionPolygons(const Shape& other, ClipperLib::PolyFillType fill_typ
     {
         return {};
     }
-    if (empty() && other.size() <= 1)
-    {
-        return other;
-    }
-    if (other.empty() && size() <= 1)
-    {
-        return *this;
-    }
+    // No further early outs, as shapes should be able to be 'unioned' with themselves, which will resolve certain issues like self-overlapping polygons.
     ClipperLib::Paths ret;
     ClipperLib::Clipper clipper(clipper_init);
     addPaths(clipper, ClipperLib::ptSubject);
@@ -203,14 +196,7 @@ Shape Shape::unionPolygons(const Polygon& polygon, ClipperLib::PolyFillType fill
     {
         return {};
     }
-    if (empty())
-    {
-        return Shape(polygon);
-    }
-    if (polygon.empty() && size() <= 1)
-    {
-        return *this;
-    }
+    // No further early outs, as unioning even with another empty polygon has some beneficial side-effects, such as removing self-overlapping polygons.
     ClipperLib::Paths ret;
     ClipperLib::Clipper clipper(clipper_init);
     addPaths(clipper, ClipperLib::ptSubject);