[FIX] base, web: set 304 status in binary_content

Before this commit, the No Change status wasn't properly set because
the `filehash` wasn't passed to `_binary_set_headers` and because
the status was not changed to 304 if it was already set to 200 earlier.

This commit fixes this issue and also prevents images to be processed
in `content_image` if the status is 304.

opw-2008426

closes odoo/odoo#34032

Signed-off-by: Christophe Simonis <chs@odoo.com>