Debug flags; stop reading ops on no data.
Crash search for 'result.soffice-ops-crash'

The crash happens after header_sort_all() sorted in memory order, and therefore [free][x][x], which then does a faulty slide/compact.

    $ gdb --args ./plot_rmalloc_compacting --peakmem result.soffice-ops-crash

For this test case, it happens specifically at the _second_ compact.
(where it actually does something.)
Fix header sort; debugging code