Errors taking place early on in startup trigger method calls on undefined objects

If an error occurs early in the startup process garbage_collection in functions.php will be called without $phpbb_dispatcher defined, so it needs to be called conditionally if the object is not NULL.

If an error occurs early in the startup process send_status_line() is used before $request is defined. This means that the protocol determination needs to fallback to HTTP/1.0 also if $request is undefined and thus not available for identifying the SERVER_PROTOCOL.