Attachment::getFilename() may be null on inline-att, widen return type

[wujku]

Inline attachments may not have both 'filename' and 'name' parameters.
In this case getFilename() returns \TypeError.

[Slamdunk]

Please:

1. Change base branch from master to v1.0
2. Add tests so we are not going to be tempted to readd the typehint again in the future

[Slamdunk]

@wujku To change the base branch you can follow the Github guide, ping me if you need help.

[Slamdunk]

Thank you @wujku

[wujku]

@Slamdunk Do you merge this with master branch?

[Slamdunk]

Of course: master represents the development branch, vX.X the current stable branch, like v1.0. New feature should be pushed in master (like your previous ones), bugfixes like this one in v1.0.
Once merged, all bugfixes are always merged in the development branch (by hand in CLI).

[Slamdunk]

1. Bugfix released in 1.0.3 tag
2. Changes merged in master with 37b2945