Avoid command line parsing error in getprefix()

Several setup command line options like --help, raise an AttributeError
exception --> just pass as in that case command line options are not
useful to determine prefix.

setup.py

@@ -151,7 +151,7 @@ class DataFilesHelper():
         dist.parse_config_files()
         try:
             dist.parse_command_line()
-        except distutils.errors.DistutilsArgError:
+        except (distutils.errors.DistutilsArgError, AttributeError):
             pass
         command = dist.get_command_obj('install')
         command.ensure_finalized()