The opm-common reader only reads unified restart files (UNRST). When the
opm-common reader was selected in preferences, cases with one restart file per
time step (X0000, X0001, ...) were opened without dynamic results.
- Fall back to the resdata reader when there is no unified restart file but
non-unified restart files are present.
- Unit tests using dynamic results check that the result and time step exist
before accessing them, so a missing result fails the test instead of
crashing the test executable.