We set the `gridX` argument of `_FortranACUFLaunchKernel` to `-1` when
`*` is passed to the grid parameter. We store it in one of `dim3`
members. However, `dim3` members are unsigned, so positive-value checks
we use later, such as `gridDim.x > 0`, are invalid. This PR utilizes the
original gird-size arguments to compute the number of blocks.
