Blender Git Loki

Fix T83888: Ctrl F in Asset Browser crashes blender

In case of being in Asset browsing mode, the search field is located in
the header (RGN_TYPE_HEADER not RGN_TYPE_UI as for file browsing mode).
To be future proof, now iterate all regions and act if the
"filter_search" can be activated.

Maniphest Tasks: T83888

Differential Revision: https://developer.blender.org/D9882