util: fix premature exit in dump mode

util: fix premature exit in dump mode

The program would end when epoll reported no ready file descriptors.
This was incorrect as data could still be awaiting to be put into
the fd when dlogutil read data from a pipe faster than dlog_logger
could feed it. Android Logger relied on this behaviour to exit when
there were no logs to read as there would not be a read() to trigger
the exit through its regular "log_len quota filled" exit path, but is
otherwise unaffected.

Change-Id: I58abc94dba9d161de684a73fe585b3efa764d0f8
Signed-off-by: Michal Bloch <m.bloch@samsung.com>