Fix potential crash in [SPSession -logout:]
Fix potential crash in [SPSession -logout:]

yingwang/Fspot,andyvand/cocoalibspotify,spotify/cocoalibspotify,CrowdTunes/cocoalibspotify,CrowdTunes/cocoalibspotify,yingwang/Fspot,CrowdTunes/cocoalibspotify,spotify/cocoalibspotify,spectralmind/cocoalibspotify,andyvand/cocoalibspotify,spectralmind/cocoalibspotify,andyvand/cocoalibspotify,yingwang/Fspot,andyvand/cocoalibspotify,spotify/cocoalibspotify,CrowdTunes/cocoalibspotify,spectralmind/cocoalibspotify,spectralmind/cocoalibspotify,spotify/cocoalibspotify