With commit 07de90466b9bf20b5ddca52680c2a902aac0b6c6 the zip-file of an
external Plugin is closed when being opened in the Manifest-Editor, but
the closing of that file must not happen before the Editor is full
opened and all content is read. Otherwise a "zip file closed" exception
is thrown and the Editor can only show that exception.

Besides fixing the mentioned issue, other ZipFiles are also closed via a
try-with-resources block.