sys/net/gnrc: gnrc_zep: fix nullPointer error
sys/net/gnrc: gnrc_zep: fix nullPointer error

kb2ma/RIOT,Josar/RIOT,roberthartung/RIOT,syin2/RIOT,RIOT-OS/RIOT,hamilton-mote/RIOT-OS,kerneltask/RIOT,rfuentess/RIOT,Hyungsin/RIOT-OS,hamilton-mote/RIOT-OS,smlng/RIOT,ant9000/RIOT,jfischer-phytec-iot/RIOT,smlng/RIOT,kb2ma/RIOT,gebart/RIOT,immesys/RiSyn,foss-for-synopsys-dwc-arc-processors/RIOT,basilfx/RIOT,A-Paul/RIOT,LudwigKnuepfer/RIOT,lazytech-org/RIOT,dkm/RIOT,BytesGalore/RIOT,thomaseichinger/RIOT,ks156/RIOT,A-Paul/RIOT,authmillenon/RIOT,LudwigOrtmann/RIOT,adjih/RIOT,adjih/RIOT,cladmi/RIOT,basilfx/RIOT,adrianghc/RIOT,gautric/RIOT,dkm/RIOT,authmillenon/RIOT,OlegHahm/RIOT,toonst/RIOT,jasonatran/RIOT,LudwigKnuepfer/RIOT,aeneby/RIOT,authmillenon/RIOT,katezilla/RIOT,kaleb-himes/RIOT,A-Paul/RIOT,beurdouche/RIOT,jbeyerstedt/RIOT-OTA-update,kerneltask/RIOT,x3ro/RIOT,kaleb-himes/RIOT,ant9000/RIOT,ks156/RIOT,plushvoxel/RIOT,RIOT-OS/RIOT,neumodisch/RIOT,biboc/RIOT,Hyungsin/RIOT-OS,Josar/RIOT,plushvoxel/RIOT,plushvoxel/RIOT,dkm/RIOT,jbeyerstedt/RIOT-OTA-update,mtausig/RIOT,gebart/RIOT,TobiasFredersdorf/RIOT,ant9000/RIOT,Josar/RIOT,yogo1212/RIOT,kYc0o/RIOT,rfuentess/RIOT,Josar/RIOT,rfuentess/RIOT,OTAkeys/RIOT,LudwigOrtmann/RIOT,neiljay/RIOT,alignan/RIOT,toonst/RIOT,biboc/RIOT,miri64/RIOT,aeneby/RIOT,basilfx/RIOT,adjih/RIOT,jbeyerstedt/RIOT-OTA-update,Hyungsin/RIOT-OS,d00616/RIOT,dkm/RIOT,gebart/RIOT,OlegHahm/RIOT,miri64/RIOT,avmelnikoff/RIOT,mtausig/RIOT,Ell-i/RIOT,jbeyerstedt/RIOT-OTA-update,BytesGalore/RIOT,jfischer-phytec-iot/RIOT,dailab/RIOT,kerneltask/RIOT,lazytech-org/RIOT,aeneby/RIOT,katezilla/RIOT,RIOT-OS/RIOT,d00616/RIOT,dailab/RIOT,biboc/RIOT,katezilla/RIOT,dailab/RIOT,adrianghc/RIOT,jfischer-phytec-iot/RIOT,x3ro/RIOT,syin2/RIOT,immesys/RiSyn,syin2/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,aeneby/RIOT,thomaseichinger/RIOT,jasonatran/RIOT,avmelnikoff/RIOT,kaleb-himes/RIOT,LudwigOrtmann/RIOT,beurdouche/RIOT,mtausig/RIOT,katezilla/RIOT,LudwigOrtmann/RIOT,LudwigKnuepfer/RIOT,thomaseichinger/RIOT,plushvoxel/RIOT,BytesGalore/RIOT,mtausig/RIOT,LudwigOrtmann/RIOT,Ell-i/RIOT,kaspar030/RIOT,backenklee/RIOT,kaspar030/RIOT,OTAkeys/RIOT,roberthartung/RIOT,LudwigKnuepfer/RIOT,RIOT-OS/RIOT,d00616/RIOT,miri64/RIOT,josephnoir/RIOT,cladmi/RIOT,tfar/RIOT,kYc0o/RIOT,adrianghc/RIOT,neiljay/RIOT,beurdouche/RIOT,BytesGalore/RIOT,backenklee/RIOT,yogo1212/RIOT,neumodisch/RIOT,neiljay/RIOT,kaleb-himes/RIOT,yogo1212/RIOT,authmillenon/RIOT,roberthartung/RIOT,biboc/RIOT,TobiasFredersdorf/RIOT,TobiasFredersdorf/RIOT,josephnoir/RIOT,backenklee/RIOT,alignan/RIOT,Josar/RIOT,x3ro/RIOT,plushvoxel/RIOT,kYc0o/RIOT,gebart/RIOT,d00616/RIOT,smlng/RIOT,yogo1212/RIOT,A-Paul/RIOT,backenklee/RIOT,RIOT-OS/RIOT,alignan/RIOT,OlegHahm/RIOT,BytesGalore/RIOT,gebart/RIOT,avmelnikoff/RIOT,mfrey/RIOT,katezilla/RIOT,ant9000/RIOT,jfischer-phytec-iot/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,basilfx/RIOT,kYc0o/RIOT,toonst/RIOT,smlng/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,neumodisch/RIOT,mfrey/RIOT,kYc0o/RIOT,Ell-i/RIOT,LudwigOrtmann/RIOT,ant9000/RIOT,toonst/RIOT,mtausig/RIOT,immesys/RiSyn,roberthartung/RIOT,neiljay/RIOT,jasonatran/RIOT,tfar/RIOT,adjih/RIOT,smlng/RIOT,hamilton-mote/RIOT-OS,OTAkeys/RIOT,lazytech-org/RIOT,dkm/RIOT,beurdouche/RIOT,TobiasFredersdorf/RIOT,x3ro/RIOT,gautric/RIOT,biboc/RIOT,immesys/RiSyn,avmelnikoff/RIOT,miri64/RIOT,gautric/RIOT,x3ro/RIOT,OlegHahm/RIOT,alignan/RIOT,kaspar030/RIOT,cladmi/RIOT,authmillenon/RIOT,lazytech-org/RIOT,A-Paul/RIOT,kerneltask/RIOT,d00616/RIOT,backenklee/RIOT,kerneltask/RIOT,kb2ma/RIOT,gautric/RIOT,yogo1212/RIOT,adjih/RIOT,TobiasFredersdorf/RIOT,syin2/RIOT,rfuentess/RIOT,ks156/RIOT,cladmi/RIOT,basilfx/RIOT,syin2/RIOT,Ell-i/RIOT,Hyungsin/RIOT-OS,OTAkeys/RIOT,kb2ma/RIOT,dailab/RIOT,kaspar030/RIOT,OlegHahm/RIOT,kbumsik/RIOT,immesys/RiSyn,ks156/RIOT,tfar/RIOT,immesys/RiSyn,Hyungsin/RIOT-OS,jasonatran/RIOT,toonst/RIOT,authmillenon/RIOT,mfrey/RIOT,kbumsik/RIOT,kb2ma/RIOT,adrianghc/RIOT,tfar/RIOT,thomaseichinger/RIOT,kaleb-himes/RIOT,kbumsik/RIOT,Ell-i/RIOT,jfischer-phytec-iot/RIOT,avmelnikoff/RIOT,gautric/RIOT,miri64/RIOT,neumodisch/RIOT,neiljay/RIOT,hamilton-mote/RIOT-OS,josephnoir/RIOT,jasonatran/RIOT,beurdouche/RIOT,OTAkeys/RIOT,roberthartung/RIOT,d00616/RIOT,kbumsik/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,ks156/RIOT,josephnoir/RIOT,tfar/RIOT,hamilton-mote/RIOT-OS,josephnoir/RIOT,LudwigKnuepfer/RIOT,alignan/RIOT,aeneby/RIOT,lazytech-org/RIOT,mfrey/RIOT,neumodisch/RIOT,dailab/RIOT,neumodisch/RIOT,adrianghc/RIOT,kaspar030/RIOT,yogo1212/RIOT,cladmi/RIOT,jbeyerstedt/RIOT-OTA-update,mfrey/RIOT,rfuentess/RIOT,kbumsik/RIOT,thomaseichinger/RIOT