Fix clearNextRange so it checks buffer properly
Created by: epiclabsDASH
Fix a regression detected in clearNextRange (BufferController). First "if", responsible of checking whether there is a buffer and ranges to clear, was wrong and always returned false what caused inconsistencies in the Media Buffer.
This is a fix for #2556 (closed). @bbert, @nicosang, could you please let me know if you can still reproduce any issue in your end? Your opinion and feedback is highly appreciated.