Fixes P2VectorToP1ScalarOperator::toMatrix()

The method was broken for 3D. We need to call getDimension() on the source
function to see whether we have a 3D setting. The destination function
represents a scalar field and, thus, we always get a 1 back.

src/hyteg/mixedoperators/P2VectorToP1ScalarOperator.hpp

@@ -63,7 +63,7 @@ class P2VectorToP1ScalarOperator : public Operator< P2VectorFunction< real_t >,
    {
       operX.toMatrix( mat, src[0], dst, level, flag );
       operY.toMatrix( mat, src[1], dst, level, flag );
-      if ( dst.getDimension() == 3 )
+      if ( src.getDimension() == 3 )
          operZ.toMatrix( mat, src[2], dst, level, flag );
    }