main: fix inverted conditional in active console reading code

We were failing when read succeeded, not when it failed, so
we were always reverting to fallback.

src/main.c

@@ -1892,7 +1892,7 @@ add_consoles_from_file (state_t         *state,
     }
 
   ply_trace ("reading file");
-  if (read (fd, contents, sizeof (contents)))
+  if (read (fd, contents, sizeof (contents)) <= 0)
     {
       ply_trace ("couldn't read it: %m");
       close (fd);