degesch: fix /query

It changed the buffer, which saved the state, which saved the line
currently being processed (thanks Readline, so obvious).

degesch.c

@@ -7626,6 +7626,8 @@ on_readline_input (char *line)
 		if (*line)
 			add_history (line);
 
+		// The text is deleted _afterwards_
+		rl_delete_text (0, rl_end);
 		process_input (ctx, line);
 		free (line);
 	}