HttpRequest.body raises ValueError for malformed CONTENT_LENGTH

[bankai]

Accessing request.body raises an unhandled ValueError when
METACONTENT_LENGTH isn't a valid integer:

ValueError: invalid literal for int() with base 10: '10,20'

This can happen with ASGIRequest if duplicate Content-Length headers are
comma-joined into a single META value. Even when such requests are usually
rejected by common HTTP parsers, HttpRequest.body is currently inconsistent
with other Django code paths.

WSGIRequest.init(), MultiPartParser.init(), and
django.core.servers.basehttp all wrap int(CONTENT_LENGTH) in:

try:

...

except (ValueError, TypeError):

content_length = 0

HttpRequest.body is the only place that calls int(CONTENT_LENGTH) without
that guard.

Minimal reproduction:

from io import BytesIO
from django.core.handlers.asgi import ASGIRequest
from django.test import AsyncRequestFactory

scope = AsyncRequestFactory()._base_scope(method="POST", path="/")
scopeheaders = [

(b"content-type", b"text/plain"),
(b"content-length", b"10,20"),

]

ASGIRequest(scope, BytesIO(b"hello world body")).body

Expected behavior:
request.body should handle malformed CONTENT_LENGTH consistently with
WSGIRequest and MultiPartParser, falling back to 0 instead of surfacing a
raw ValueError.

Actual behavior:
request.body raises ValueError.

I have a patch and regression test.