Fix T71019: Disappearing file thumbnails & crash on area split

When opening the file browser as regular editor, the ID filter flags
as stored in FileSelectParams were not set explicitly, so they were 0.
Since 9100982e80, the value actually passed to the filtering could
differ from that, causing the file list cache to be constantly updated
on every redraw.

Caused by 9100982e80.

Note that this "accidentially" got fixed in master with b546263642,
which is why the issue only showed up in the release branch from that
point.

source/blender/editors/space_file/filesel.c

@@ -107,6 +107,7 @@ short ED_fileselect_set_params(SpaceFile *sfile)
     sfile->params->thumbnail_size = U_default.file_space_data.thumbnail_size;
     /* Show size column by default. */
     sfile->params->details_flags = U_default.file_space_data.details_flags;
+    sfile->params->filter_id = FILTER_ID_ALL;
   }
 
   params = sfile->params;
@@ -246,9 +247,6 @@ short ED_fileselect_set_params(SpaceFile *sfile)
       }
     }
 
-    /* For now, always init filterid to 'all true' */
-    params->filter_id = FILTER_ID_ALL;
-
     if (U.uiflag & USER_HIDE_DOT) {
       params->flag |= FILE_HIDE_DOT;
     }