Knife project switches out of vertex selection mode, but wouldnt do this
for all participating meshes.
Logic in edbm_select_linked_pick would switch the viewcontext multiple
times and the meshes selectmode was not in sync then, leading e.g.
finding a vertex in 'unified_findnearest' (because last of the meshes
selectmode was SCE_SELECT_VERTEX), but then later in
'EDBM_elem_from_selectmode' other meshes selectmode was not matching
SCE_SELECT_VERTEX, leading to crash...
Reviewers: campbellbarton
Maniphest Tasks: T68852
Differential Revision: https://developer.blender.org/D5536
6f4e595e9b