(read_process_output): Fix the args CHARPOS and LENINS

to signal_after_change.

src/process.c

@@ -3181,7 +3181,7 @@ read_process_output (proc, channel)
       else
 	{
 	  insert_1_both (chars, nchars, nbytes, 0, 1, 1);
-	  signal_after_change (opoint, 0, PT - opoint);
+	  signal_after_change (before, 0, PT - before);
 	  update_compositions (before, PT, CHECK_BORDER);
 	}
       set_marker_both (p->mark, p->buffer, PT, PT_BYTE);