[project.py] Preventing a traceback when a library is not built during export
[project.py] Preventing a traceback when a library is not built during export

adustm/mbed,arostm/mbed-os,CalSol/mbed,karsev/mbed-os,RonEld/mbed,kl-cruz/mbed-os,fanghuaqi/mbed,betzw/mbed-os,bulislaw/mbed-os,adustm/mbed,arostm/mbed-os,YarivCol/mbed-os,kl-cruz/mbed-os,tung7970/mbed-os,mikaleppanen/mbed-os,c1728p9/mbed-os,Archcady/mbed-os,adustm/mbed,nRFMesh/mbed-os,betzw/mbed-os,j-greffe/mbed-os,jeremybrodt/mbed,tung7970/mbed-os-1,karsev/mbed-os,cvtsi2sd/mbed-os,fahhem/mbed-os,svogl/mbed-os,mbedmicro/mbed,netzimme/mbed-os,adamgreen/mbed,monkiineko/mbed-os,c1728p9/mbed-os,monkiineko/mbed-os,mmorenobarm/mbed-os,kjbracey-arm/mbed,cvtsi2sd/mbed-os,catiedev/mbed-os,pradeep-gr/mbed-os5-onsemi,andreaslarssonublox/mbed,infinnovation/mbed-os,j-greffe/mbed-os,maximmbed/mbed,monkiineko/mbed-os,CalSol/mbed,monkiineko/mbed-os,mmorenobarm/mbed-os,YarivCol/mbed-os,CalSol/mbed,screamerbg/mbed,infinnovation/mbed-os,infinnovation/mbed-os,kl-cruz/mbed-os,catiedev/mbed-os,RonEld/mbed,nRFMesh/mbed-os,nvlsianpu/mbed,jeremybrodt/mbed,betzw/mbed-os,andcor02/mbed-os,geky/mbed,rgrover/mbed,netzimme/mbed-os,pradeep-gr/mbed-os5-onsemi,jeremybrodt/mbed,bulislaw/mbed-os,rgrover/mbed,screamerbg/mbed,HeadsUpDisplayInc/mbed,bulislaw/mbed-os,monkiineko/mbed-os,svogl/mbed-os,geky/mbed,YarivCol/mbed-os,radhika-raghavendran/mbed-os5.1-onsemi,nvlsianpu/mbed,nvlsianpu/mbed,cvtsi2sd/mbed-os,netzimme/mbed-os,bulislaw/mbed-os,CalSol/mbed,nvlsianpu/mbed,adamgreen/mbed,NXPmicro/mbed,pradeep-gr/mbed-os5-onsemi,mmorenobarm/mbed-os,bulislaw/mbed-os,adamgreen/mbed,betzw/mbed-os,fanghuaqi/mbed,andreaslarssonublox/mbed,fahhem/mbed-os,kl-cruz/mbed-os,j-greffe/mbed-os,svogl/mbed-os,adamgreen/mbed,kjbracey-arm/mbed,maximmbed/mbed,fanghuaqi/mbed,Archcady/mbed-os,RonEld/mbed,ryankurte/mbed-os,maximmbed/mbed,svastm/mbed,fvincenzo/mbed-os,Archcady/mbed-os,YarivCol/mbed-os,screamerbg/mbed,ryankurte/mbed-os,geky/mbed,fahhem/mbed-os,andcor02/mbed-os,nRFMesh/mbed-os,kjbracey-arm/mbed,andreaslarssonublox/mbed,j-greffe/mbed-os,svastm/mbed,ryankurte/mbed-os,NXPmicro/mbed,CalSol/mbed,pradeep-gr/mbed-os5-onsemi,andreaslarssonublox/mbed,infinnovation/mbed-os,andcor02/mbed-os,karsev/mbed-os,tung7970/mbed-os,NXPmicro/mbed,kjbracey-arm/mbed,radhika-raghavendran/mbed-os5.1-onsemi,adustm/mbed,mazimkhan/mbed-os,svastm/mbed,bcostm/mbed-os,geky/mbed,nvlsianpu/mbed,bulislaw/mbed-os,Archcady/mbed-os,c1728p9/mbed-os,fvincenzo/mbed-os,catiedev/mbed-os,karsev/mbed-os,HeadsUpDisplayInc/mbed,ryankurte/mbed-os,mmorenobarm/mbed-os,jeremybrodt/mbed,c1728p9/mbed-os,nRFMesh/mbed-os,YarivCol/mbed-os,arostm/mbed-os,mazimkhan/mbed-os,YarivCol/mbed-os,c1728p9/mbed-os,screamerbg/mbed,HeadsUpDisplayInc/mbed,mbedmicro/mbed,mbedmicro/mbed,rgrover/mbed,mazimkhan/mbed-os,catiedev/mbed-os,mazimkhan/mbed-os,netzimme/mbed-os,theotherjimmy/mbed,tung7970/mbed-os-1,mazimkhan/mbed-os,rgrover/mbed,netzimme/mbed-os,nRFMesh/mbed-os,bcostm/mbed-os,svastm/mbed,bcostm/mbed-os,ryankurte/mbed-os,betzw/mbed-os,fvincenzo/mbed-os,j-greffe/mbed-os,netzimme/mbed-os,andcor02/mbed-os,tung7970/mbed-os,infinnovation/mbed-os,NXPmicro/mbed,bcostm/mbed-os,fvincenzo/mbed-os,monkiineko/mbed-os,betzw/mbed-os,RonEld/mbed,tung7970/mbed-os-1,mmorenobarm/mbed-os,HeadsUpDisplayInc/mbed,fahhem/mbed-os,cvtsi2sd/mbed-os,karsev/mbed-os,maximmbed/mbed,andcor02/mbed-os,radhika-raghavendran/mbed-os5.1-onsemi,CalSol/mbed,radhika-raghavendran/mbed-os5.1-onsemi,RonEld/mbed,c1728p9/mbed-os,adamgreen/mbed,rgrover/mbed,NXPmicro/mbed,Archcady/mbed-os,adustm/mbed,mikaleppanen/mbed-os,nRFMesh/mbed-os,arostm/mbed-os,tung7970/mbed-os-1,Archcady/mbed-os,theotherjimmy/mbed,tung7970/mbed-os-1,screamerbg/mbed,cvtsi2sd/mbed-os,andreaslarssonublox/mbed,maximmbed/mbed,svogl/mbed-os,theotherjimmy/mbed,mbedmicro/mbed,adamgreen/mbed,j-greffe/mbed-os,HeadsUpDisplayInc/mbed,kl-cruz/mbed-os,tung7970/mbed-os,fahhem/mbed-os,svastm/mbed,svogl/mbed-os,radhika-raghavendran/mbed-os5.1-onsemi,mazimkhan/mbed-os,ryankurte/mbed-os,nvlsianpu/mbed,mikaleppanen/mbed-os,NXPmicro/mbed,svogl/mbed-os,catiedev/mbed-os,pradeep-gr/mbed-os5-onsemi,bcostm/mbed-os,arostm/mbed-os,bcostm/mbed-os,RonEld/mbed,fvincenzo/mbed-os,mmorenobarm/mbed-os,karsev/mbed-os,jeremybrodt/mbed,theotherjimmy/mbed,mbedmicro/mbed,mikaleppanen/mbed-os,theotherjimmy/mbed,theotherjimmy/mbed,screamerbg/mbed,tung7970/mbed-os,fanghuaqi/mbed,arostm/mbed-os,pradeep-gr/mbed-os5-onsemi,cvtsi2sd/mbed-os,HeadsUpDisplayInc/mbed,catiedev/mbed-os,fanghuaqi/mbed,infinnovation/mbed-os,adustm/mbed,andcor02/mbed-os,geky/mbed,mikaleppanen/mbed-os,kl-cruz/mbed-os,mikaleppanen/mbed-os,radhika-raghavendran/mbed-os5.1-onsemi,fahhem/mbed-os,maximmbed/mbed