Read 2D chemistry probe species after locating the probe

[sbryngelson]

In the 2D branch of s_write_probe_files the species partial densities
were read from q_cons_vf(j-2, k-2, l) before j, k and l were computed
for the current probe and outside the ownership check, so they used the
previous probe's cell or, for the first probe, uninitialized indices.
A gfortran debug run of a 2D chemistry case with probes aborted on an
out-of-bounds index.

Move the read inside the ownership branch after the indices are set,
as in the 1D and 3D branches.

[sbryngelson]

Closing this for now to bring the number of open PRs from me down to four, so the ones that stay open get real review attention rather than being lost in a queue of 35.

No work is lost and nothing needs re-doing. The branch fix/2d-chem-probe-indices remains on the fork at 8381419e38, this PR's diff and discussion stay here, and the head commit is additionally archived in a local verified bundle. Reopening takes no force-push and no rebase:

gh pr reopen 1989 -R MFlowCode/MFC

I intend to reopen these in small batches as the open slots free up. Apologies for the notification noise.

Opened and closed with Claude Code.