liblog: remove code checking for fd = 0

Fix a typo where I check socket()'s return value for 0 instead of -1
as an error.

Remove code that checks if socket() returns 0 as the actual fd that it
returns.  This should not happen in any well formed program.

Test: liblog unit tests
Change-Id: I1d878e85d9a39155d68c6c84e9cf9b0db8d1b3a4