liblog: reject empty logging messages

A regression after "liblog: Instrument logging of logd write drops"
where an empty payload would result in an insufficient iovec to
report the write drop.

Change-Id: Iffabcfbb0680898d7a42004700e638e9d940ff5f
1 file changed
tree: 6f2c149341abec58b8ef7d4b4e456c83f62f2c6d
  1. liblog/
  2. logcat/
  3. logd/
  4. logwrapper/