fix PackagePart.GetRelationships for readonly files

Fixes this bug: https://bugzilla.novell.com/show_bug.cgi?id=675379

'PackagePart.GetRelationships throws an "Operation not valid when package is read-only" exception when package is open with only read presmissions'
Please add a space after `GetPart` (before the opening parenthesis) like in the rest of the code. There's also an unnecessary space after `part`.