Fix removing attachments on edit-post
Fix removing attachments on edit-post

Seems like a bug after the recent refactoring, `this.id` on line 448
doesn't work correctly, so this change provides correct `this` there.

Fixes #29.

golozubov/freefeed-server,FreeFeed/freefeed-server,SiTLar/freefeed-server,FreeFeed/freefeed-server,SiTLar/freefeed-server,davidmz/pepyatka-server,golozubov/freefeed-server