Change avatar may fail on multi-user system

[david douard]

If 2 persons logged on the same Unix system wants to change their avator pict, it will fail if gajim create a '/tmp/avatar_scaled.png' for person A (it does not remove it after use), and user B does the same a short time after. The file then exists, owner by A, thus B cannot write it.

Attached is a small patch to assert this.

David

[david.douard at gmail.com]

patch file for the reported bug

[asterix]

(In [7826]) remove temp file once we don't need it anymore. fixes #2894