don't die silently when owncloud log cannot be initialized

Just faced the white screen of death because the permissions of the data folder were borked ... as a result the owncloud log class could not be initialized. A @ prevented any error from showing up and then I got the following log:
```

[Tue Feb 18 12:19:45.453385 2014] [:error] [pid 9803] [client ::1:57190] PHP Fatal error:  Call to a member function debug() on a non-object in /home/jfd/Repositories/oc/core/lib/private/log/errorhandler.php on line 71
[Tue Feb 18 12:19:45.453440 2014] [:error] [pid 9803] [client ::1:57190] PHP Stack trace:
[Tue Feb 18 12:19:45.453536 2014] [:error] [pid 9803] [client ::1:57190] PHP   1. {main}() /home/jfd/Repositories/oc/core/index.php:0
[Tue Feb 18 12:19:45.453584 2014] [:error] [pid 9803] [client ::1:57190] PHP   2. require_once() /home/jfd/Repositories/oc/core/index.php:28
[Tue Feb 18 12:19:45.453646 2014] [:error] [pid 9803] [client ::1:57190] PHP   3. OC::init() /home/jfd/Repositories/oc/core/lib/base.php:975
[Tue Feb 18 12:19:45.453689 2014] [:error] [pid 9803] [client ::1:57190] PHP   4. spl_autoload_call(*uninitialized*) /home/jfd/Repositories/oc/core/lib/base.php:512
[Tue Feb 18 12:19:45.453766 2014] [:error] [pid 9803] [client ::1:57190] PHP   5. OC\\Autoloader->load($class = *uninitialized*) /home/jfd/Repositories/oc/core/lib/base.php:0
[Tue Feb 18 12:19:45.453808 2014] [:error] [pid 9803] [client ::1:57190] PHP   6. require_once() /home/jfd/Repositories/oc/core/lib/autoloader.php:143
[Tue Feb 18 12:19:45.453866 2014] [:error] [pid 9803] [client ::1:57190] PHP   7. OC\\Log->__construct() /home/jfd/Repositories/oc/core/lib/private/legacy/log.php:16
[Tue Feb 18 12:19:45.453908 2014] [:error] [pid 9803] [client ::1:57190] PHP   8. call_user_func(*uninitialized*) /home/jfd/Repositories/oc/core/lib/private/log.php:117
[Tue Feb 18 12:19:45.453966 2014] [:error] [pid 9803] [client ::1:57190] PHP   9. OC_Log_Owncloud::init() /home/jfd/Repositories/oc/core/lib/private/log.php:117
[Tue Feb 18 12:19:45.454008 2014] [:error] [pid 9803] [client ::1:57190] PHP  10. touch(*uninitialized*) /home/jfd/Repositories/oc/core/lib/private/log/owncloud.php:48
[Tue Feb 18 12:19:45.454133 2014] [:error] [pid 9803] [client ::1:57190] PHP  11. OC\\Log\\ErrorHandler->onAll($number = *uninitialized*, $message = *uninitialized*, $file = *uninitialized*, $line = *uninitialized*, *uninitialized*) /home/jfd/Repositories/oc/core/lib/private/log/owncloud.php:48
```

@DeepDiver1975 @PVince81 please review