[FIX] ir_http: return a 404 if binary content cannot be decoded

Backport of a68f7e6e

Commit 5a9e1af6 has the unfortunate side-effect of crashing early
if for any reason the content cannot be decoded.
However, simply ignoring that the content cannot be decoded is no better idea:
some functions pipe the result to decoding functions that crash the same.
The resulting traceback pollutes the log with uninformative message such as:
binascii.Error: Incorrect padding 5 0.002 0.016

In case the content cannot be decoded (data corruption, or simply missing file)
we return a clean 404 instead, which is morally almost equivalent,
and is clean even from functions that depend on binary_content.

opw 2117114

closes odoo/odoo#39792

Signed-off-by: Nans Lefebvre (len) <len@odoo.com>