devd: correct two warnings

- catching a polymorphic type by value
- "output between 16 and 95 bytes into a destination of size 80"

sbin/devd/devd.cc

@@ -1087,7 +1087,7 @@ event_loop(void)
 				try {
 					process_event(buffer);
 				}
-				catch (std::length_error e) {
+				catch (const std::length_error& e) {
 					devdlog(LOG_ERR, "Dropping event %s "
 					    "due to low memory", buffer);
 				}

sbin/devd/tests/client_test.c

@@ -50,7 +50,7 @@ create_two_events(void)
 	FILE *create_stdout;
 	FILE *destroy_stdout;
 	char mdname[80];
-	char destroy_cmd[80];
+	char destroy_cmd[95];
 	char *error;
 
 	create_stdout = popen("mdconfig -a -s 64 -t null", "r");