BUG: fixed SAS7BDATReader._get_properties
this fixes a crasher I had in one of my files using SAS7BDATReader.

cc: @kshedden 

self._path_or_buf.read is an obvious mistake

also added + total_align to _os_name_offset and _os_make_offset as they are
present in the original code from Jared Hobbs:
https://bitbucket.org/jaredhobbs/sas7bdat/src/da1faa90d0b15c2c97a2a8eb86c91c58081bdd86/sas7bdat.py?fileviewer=file-view-default#sas7bdat.py-1450
