vPreProcess attempts stereo undistortion, even when only a single camera intrinsics are supplied

[lunagava]

The zynqGrabber module sends to vPreProcess both left and right output, unless you set --visLeftOn or --visRightOn to false. When undistortion parameter inside vPreProcess is set to true, the function sparseForwardTransform(int cam, int &y, int &x) inside vIPT.cpp crashes as soon as you connect /zynqGrabber/AE:o to /vPreProcess/AE:i (for the non existing camera).