multipart upload: ignore trailing-newline requirement from spec

multipart upload: ignore trailing-newline requirement from spec

Allow upload without trailing newline, even though this is not
compliant with RFC 1521.

RFC 1521 mandates that the close-delimiter ends in a newline:
'close-delimiter := "--" boundary "--" CRLF'

However, some software (e.g. postman) sends their request without a
trailing newline, which resulted in failing uploads.

Signed-off-by: Matthias Heiserer <m.heiserer@proxmox.com>
Reviewed-by: Daniel Tschlatscher <d.tschlatscher@proxmox.com>
Tested-by:  Daniel Tschlatscher <d.tschlatscher@proxmox.com>