Unnecessary calculations which add then subtract same variable

[swdee]

In the following code there are unnecessary calculations being performed as the same variable cancels itself out.

ByteTrack-cpp/src/Rect.cpp

Line 121 in d43805d

const float ua = (tlwh[0] + tlwh[2] - tlwh[0] + 1) * (tlwh[1] + tlwh[3] - tlwh[1] + 1) + box_area - iw * ih;

Instead it should be.

 const float ua = (tlwh[2] + 1) * (tlwh[3] + 1) + box_area - iw * ih;