bug 1127937 - don't show duration header if value not known
bug 1127937 - don't show duration header if value not known

kenrick95/airmozilla,anjalymehla/airmozilla,a-buck/airmozilla,anu7495/airmozilla,kenrick95/airmozilla,mythmon/airmozilla,mozilla/airmozilla,tannishk/airmozilla,lcamacho/airmozilla,a-buck/airmozilla,zofuthan/airmozilla,chirilo/airmozilla,chirilo/airmozilla,lcamacho/airmozilla,ehsan/airmozilla,mythmon/airmozilla,anjalymehla/airmozilla,anu7495/airmozilla,ehsan/airmozilla,lcamacho/airmozilla,Nolski/airmozilla,tannishk/airmozilla,a-buck/airmozilla,lcamacho/airmozilla,blossomica/airmozilla,kenrick95/airmozilla,Nolski/airmozilla,blossomica/airmozilla,chirilo/airmozilla,Nolski/airmozilla,tannishk/airmozilla,kenrick95/airmozilla,tannishk/airmozilla,kenrick95/airmozilla,blossomica/airmozilla,anjalymehla/airmozilla,anjalymehla/airmozilla,zofuthan/airmozilla,a-buck/airmozilla,mythmon/airmozilla,zofuthan/airmozilla,ehsan/airmozilla,EricSekyere/airmozilla,anu7495/airmozilla,mozilla/airmozilla,tannishk/airmozilla,EricSekyere/airmozilla,zofuthan/airmozilla,anu7495/airmozilla,EricSekyere/airmozilla,Nolski/airmozilla,mozilla/airmozilla,chirilo/airmozilla,anu7495/airmozilla,ehsan/airmozilla,EricSekyere/airmozilla,mythmon/airmozilla,EricSekyere/airmozilla,ehsan/airmozilla,chirilo/airmozilla,mozilla/airmozilla,blossomica/airmozilla,lcamacho/airmozilla,mythmon/airmozilla,anjalymehla/airmozilla,Nolski/airmozilla,zofuthan/airmozilla