install-node: Fix provisioning when node/npm don't exist.
install-node: Fix provisioning when node/npm don't exist.

Our recent performance changes to this script broke it in the case
where there was no previous version of node/npm installed.

vabs22/zulip,kou/zulip,andersk/zulip,punchagan/zulip,kou/zulip,punchagan/zulip,hackerkid/zulip,shubhamdhama/zulip,mahim97/zulip,Galexrt/zulip,jrowan/zulip,kou/zulip,kou/zulip,synicalsyntax/zulip,timabbott/zulip,hackerkid/zulip,jackrzhang/zulip,timabbott/zulip,brainwane/zulip,eeshangarg/zulip,tommyip/zulip,Galexrt/zulip,tommyip/zulip,rht/zulip,synicalsyntax/zulip,vabs22/zulip,hackerkid/zulip,jrowan/zulip,hackerkid/zulip,vabs22/zulip,jackrzhang/zulip,kou/zulip,mahim97/zulip,jrowan/zulip,punchagan/zulip,eeshangarg/zulip,rht/zulip,punchagan/zulip,punchagan/zulip,showell/zulip,amanharitsh123/zulip,tommyip/zulip,timabbott/zulip,brockwhittaker/zulip,punchagan/zulip,amanharitsh123/zulip,dhcrzf/zulip,kou/zulip,vaidap/zulip,tommyip/zulip,brainwane/zulip,zulip/zulip,zulip/zulip,punchagan/zulip,vaidap/zulip,brockwhittaker/zulip,dhcrzf/zulip,synicalsyntax/zulip,timabbott/zulip,vaidap/zulip,amanharitsh123/zulip,hackerkid/zulip,rht/zulip,brainwane/zulip,hackerkid/zulip,zulip/zulip,jrowan/zulip,dhcrzf/zulip,jackrzhang/zulip,timabbott/zulip,Galexrt/zulip,synicalsyntax/zulip,Galexrt/zulip,rht/zulip,showell/zulip,vabs22/zulip,eeshangarg/zulip,mahim97/zulip,brockwhittaker/zulip,brainwane/zulip,showell/zulip,eeshangarg/zulip,amanharitsh123/zulip,brainwane/zulip,verma-varsha/zulip,rht/zulip,verma-varsha/zulip,dhcrzf/zulip,dhcrzf/zulip,synicalsyntax/zulip,shubhamdhama/zulip,amanharitsh123/zulip,jrowan/zulip,synicalsyntax/zulip,hackerkid/zulip,brockwhittaker/zulip,mahim97/zulip,jackrzhang/zulip,tommyip/zulip,rishig/zulip,timabbott/zulip,zulip/zulip,rishig/zulip,brainwane/zulip,eeshangarg/zulip,zulip/zulip,Galexrt/zulip,vaidap/zulip,zulip/zulip,showell/zulip,eeshangarg/zulip,brainwane/zulip,shubhamdhama/zulip,vabs22/zulip,verma-varsha/zulip,shubhamdhama/zulip,timabbott/zulip,rishig/zulip,andersk/zulip,andersk/zulip,jackrzhang/zulip,eeshangarg/zulip,andersk/zulip,Galexrt/zulip,dhcrzf/zulip,vaidap/zulip,zulip/zulip,amanharitsh123/zulip,rishig/zulip,tommyip/zulip,showell/zulip,kou/zulip,Galexrt/zulip,jrowan/zulip,vabs22/zulip,verma-varsha/zulip,verma-varsha/zulip,tommyip/zulip,mahim97/zulip,mahim97/zulip,showell/zulip,jackrzhang/zulip,brockwhittaker/zulip,andersk/zulip,rht/zulip,shubhamdhama/zulip,verma-varsha/zulip,shubhamdhama/zulip,brockwhittaker/zulip,andersk/zulip,shubhamdhama/zulip,jackrzhang/zulip,rht/zulip,showell/zulip,dhcrzf/zulip,rishig/zulip,synicalsyntax/zulip,rishig/zulip,vaidap/zulip,rishig/zulip,andersk/zulip