Stop hp3500 backend from calling exit() at the end of a scan (which is

unhelpful when sane threads are threads rather than processes).

backend/hp3500.c

@@ -3392,11 +3392,11 @@ reader_process (void *pv)
   sigset_t sigterm_set;
   struct SIGACTION act;
   struct hp3500_write_info winfo;
+  int status;
 
   if (sanei_thread_is_forked ())
     {
       close (scanner->pipe_r);
-    }
 
       sigfillset (&ignore_set);
       sigdelset (&ignore_set, SIGTERM);
@@ -3413,6 +3413,7 @@ reader_process (void *pv)
       act.sa_handler = sigtermHandler;
 #endif
       sigaction (SIGTERM, &act, 0);
+    }
 
 
   /* Warm up the lamp again if our last scan ended more than 5 minutes ago. */
@@ -3447,6 +3448,8 @@ reader_process (void *pv)
        scanner->actres_pixels.bottom - scanner->actres_pixels.top,
        scanner->resolution, scanner->mode, (rts8801_callback) writefunc,
        &winfo) >= 0)
-    exit (SANE_STATUS_GOOD);
-  exit (SANE_STATUS_IO_ERROR);
+    status = SANE_STATUS_GOOD;
+  status = SANE_STATUS_IO_ERROR;
+  close (scanner->pipe_w);
+  return status;
 }