Avoid signed-unsigned comparison
Avoid signed-unsigned comparison

This had the effect of the error-handling path not being used
practically ever, since the signed bytesWritten was coerced into its
large unsigned representation, although that may be compiler-specific
behavior.

Signed-off-by: Daniel Farina <3d0f3b9ddcacec30c4008c5e030e6c13a478cb4f@fdr.io>

logplex/pg_logfebe,logplex/pg_logfebe