gcoap: Fix compilation error when client token length macro set to 0.
gcoap: Fix compilation error when client token length macro set to 0.

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