invalidate all headers when re-rendering

Ifd2d3d introduced a regression when re-rendering that leaves
the existing headers around. This is bad when the new
conversation is shorter (e.g. on draft discard), or if the
messages are re-ordered (nearly simultaneous sending).

Clear header views when clearing the adapter as was done
previously.

Bug: 7422803
Bug: 7418910
Change-Id: Iba6a85d249917c8deeeaa978d2ebb8d59102c1ad
1 file changed