osd: EINVAL from truncate causes osd to crash

Maximum object size is 100GB configurable with osd_max_object_size
Error EFBIG if attempt to WRITE/WRITEFULL/TRUNCATE beyond osd_max_object_size
Error EINVAL if length < 1 for WRITE/WRITEFULL/ZERO
Make ZERO beyond existing size a no-op

Fixes: #5252
Fixes: #5340

Signed-off-by: David Zafman <david.zafman@inktank.com>