Blender Git Loki

Fix T72089: Image Editor - Paint mode, Clone Tool - disfunctional clear
button in the Image slot in the Brush panel

Caused/exposed by rBaf9ca138ba7b
Also relevant was rB828905190e12

Above commits moved the WM_UI_HANDLER_BREAK around so it would not be
returned anymore.
We need WM_UI_HANDLER_BREAK, otherwise we wont get through to to
KM_RELEASE. There are two places that explicitly check for KM_RELEASE
(call to `ui_do_but_extra_operator_icon` in both
`ui_do_but_SEARCH_UNLINK` / `ui_do_button`), and without the above we
only ever get here with KM_PRESS.

This patch restores the behavior regarding WM_UI_HANDLER_BREAK to what
is was before the two culprit commits.

Checked that both this report (T72089) and T69755 are working.

Maniphest Tasks: T72089

Differential Revision: https://developer.blender.org/D6363