Openmc nucid fix

When the cross_sections.xml for OpenMC has an entry with the ZAID field in MCNP form, (e.g. the standard cross_sections.xml in openmc/data), we attempted to get the `nucid` property of each `AceTable` by concatenating the ZA and the metastable state. However sometimes this leads to `nucid` being something wacky like 274580001 for Co-58m. So now we check if the first method gives a valid nuclide, and attempt to parse the ZAID field in MCNP form if that doesn't work.