operator= should accept const args too to make stl implementations happy

sd/source/ui/slidesorter/inc/controller/SlsTransferable.hxx

@@ -52,7 +52,7 @@ public:
             : maBitmap(rBitmap), mbIsExcluded(bIsExcluded) {}
         Representative (const Representative& rOther)
             : maBitmap(rOther.maBitmap), mbIsExcluded(rOther.mbIsExcluded) {}
-        Representative operator= (Representative& rOther)
+        Representative operator= (Representative const& rOther)
         {   if (&rOther != this) {maBitmap = rOther.maBitmap; mbIsExcluded = rOther.mbIsExcluded; }
             return *this;
         }