`build_http_response` must always update `Content-Length` header

[abhinavsingh]

Reference

proxy.py/proxy/common/utils.py

Lines 107 to 115 in 54e74a9

	for k, _ in headers.items():
	if k.lower() == b'content-length':
	has_content_length = True
	if k.lower() == b'transfer-encoding':
	has_transfer_encoding = True
	if body is not None and \
	not has_transfer_encoding and \
	not has_content_length:
	headers[b'Content-Length'] = bytes_(len(body))

If a plugin modifies the response without updating Content-Length header, client may see errors or at worst hang. build_http_response must ensure that Content-Length header matches size of response to be dispatched.