forcegraph: do not use global ctx when preparing labels
forcegraph: do not use global ctx when preparing labels

ffac/meshviewer_old,freifunk-mwu/meshviewer,nonchip/meshviewer,hopglass/ffrgb-meshviewer,FreiFunkMuenster/meshviewer,yayachiken/hopglass,tcatm/meshviewer,FreifunkMD/Meshviewer,Freifunk-Luxembourg/hopglass,tcatm/meshviewer,freifunkMUC/meshviewer,xf-/meshviewer-1,nickel715/meshviewer,tcatm/meshviewer,Freifunk-Troisdorf/meshviewer,ffac/meshviewer_old,TVLuke/meshviewer,nonchip/meshviewer,freifunk-mwu/meshviewer,freifunk-mwu/meshviewer,FreifunkBremen/meshviewer-ffrgb,rubo77/meshviewer-1,Freifunk-Luxembourg/hopglass,Freifunk-Rhein-Neckar/meshviewer,mayflower/meshviewer,ffac/meshviewer,ffnord/meshviewer,freifunk-fulda/meshviewer,hopglass/hopglass,hopglass/ffrgb-meshviewer,plumpudding/hopglass,srauscher/hopglass,FreiFunkMuenster/meshviewer,FreifunkBremen/meshviewer-ffrgb,ffrgb/meshviewer,kgbvax/meshviewer,freifunk-fulda/meshviewer,rubo77/meshviewer,ffnord/meshviewer,mayflower/meshviewer,nickel715/meshviewer,Freifunk-Troisdorf/meshviewer,rubo77/meshviewer-1,TVLuke/meshviewer,Skrupellos/meshviewer,plumpudding/hopglass,Little-Ben/meshviewer,Skrupellos/meshviewer,rubo77/meshviewer-compilation,ffnord/meshviewer,TVLuke/meshviewer,Little-Ben/meshviewer,srauscher/hopglass,hopglass/hopglass,kgbvax/meshviewer,FreifunkMD/Meshviewer,rubo77/meshviewer,ffrgb/meshviewer,ffac/meshviewer,ffac/meshviewer,Freifunk-Rhein-Neckar/meshviewer,FreiFunkMuenster/meshviewer,nonchip/meshviewer,max-weller/meshviewer,rubo77/meshviewer-compilation,Freifunk-Rhein-Neckar/meshviewer,gherber/hopglass,max-weller/meshviewer,yayachiken/hopglass,freifunkMUC/meshviewer,gherber/hopglass,xf-/meshviewer-1