Hi,

OUTPUT_DEBUG_STRING_EVENT events can happen from after the inferior
is created, until it is stopped at the initial breakpoint, waiting
for gdb.  The OUTPUT_DEBUG_STRING_EVENT handler doesn't currently
check if a remote connection is open before sending data, generating
annoying putpkt error logs to gdbserver's console.  This
patch fixes it by simply ignoring those events when there isn't any
gdb connected yet.  I didn't use server_wait, because this event
is also handled in win32_kill, outside of a wait.

Cheers,
Pedro Alves