Fix offset for vtkImageFourierCenter

The shift for vtkImageFourierCenter was off by one, placing the
spectrum one pixel past the center of the image.

Imaging/Core/Testing/Data/Baseline/Spectrum.png.sha512

-e5cae70201e7e379742c2f3aeb6f6f4fa98edcf6a3532e3798eee4a66b74c2462604268aca9ac88d79ae322f9713c1ab360895b7e0939d8638372216b11fcb51
+d13bf13a39cee76b41e2ea43c71bee70461b05e0503337a5bec19a6522acf203c029a2391853508a32ef1d82a61954b576bb2a53d1ddae75bb1b796dd89944d1

Imaging/Fourier/vtkImageFourierCenter.cxx

@@ -104,7 +104,7 @@ void vtkImageFourierCenter::ThreadedRequestData(vtkInformation* vtkNotUsed(reque
   // Determine the mid for the filtered axis
   wholeMin0 = wholeExtent[this->Iteration * 2];
   wholeMax0 = wholeExtent[this->Iteration * 2 + 1];
-  mid0 = (wholeMin0 + wholeMax0) / 2;
+  mid0 = (wholeMin0 + wholeMax0 + 1) / 2;
 
   // initialize input coordinates
   inCoords[0] = outExt[0];