CarpetIOHDF5: Don't set "delta" attribute to zero for zero-width components

[Erik Schnetter]

Carpet’s HDF5 format outputs a delta attribute that describes the grid spacing for each written chunk. Currently delta is always set to zero for zero-width components, i.e. e.g. for 2d arrays. This confuses post-processing tools.

This pull request passes the actual grid spacing to the writer routine, and writes the correct grid spacing into the attribute.

The pull request is at https://bitbucket.org/eschnett/carpet/pull-requests/46 .

[Roland Haas]

Please review.

[Roland Haas]

Please apply.

[Roland Haas]

Demo parfile showing the issue in gxx.xyz.h5 where delta is reported as "0.5, 0.5, 0" without the patch (gxx.h5 is fine however).

[Erik Schnetter]

Applied in https://bitbucket.org/eschnett/carpet/commits/73edd0639548fb158c5f196f647f280cf73e6be5.