fix data initialization

src/operator.jl

@@ -240,6 +240,7 @@ function project_img2!(u::FeFunction, img)
     # number of element dofs (i.e. local dofs not counting range dimensions)
     nldofs = ndofs(space.element)
 
+    u.data .= 0
     # count contributions to respective dof for subsequent averaging
     gdofcount = zeros(Int, size(u.data))