Fix a bug in main.js
Fix a bug in main.js

In global view, there is no ".category.all>a" element so we tried
to apply str2int on an undefined value.
In consequence, we were not able to mark several articles as read

This patch need to apply on 0.8.1 and 0.9.1

See https://github.com/marienfressinaud/FreshRSS/issues/649

plopoyop/FreshRSS,Alkarex/FreshRSS,asmundg/FreshRSS,Alkarex/FreshRSS,aledeg/FreshRSS,marienfressinaud/FreshRSS,romibi/FreshRSS,FreshRSS/FreshRSS,samuelstein/FreshRSS,Dolomich/FreshRSS,asmundg/FreshRSS,aledeg/FreshRSS,asmundg/FreshRSS,superboum/FreshRSS,Dolomich/FreshRSS,Alkarex/FreshRSS,aledeg/FreshRSS,marienfressinaud/FreshRSS,romibi/FreshRSS,superboum/FreshRSS,aledeg/FreshRSS,samuelstein/FreshRSS,samuelstein/FreshRSS,plopoyop/FreshRSS,marienfressinaud/FreshRSS,FreshRSS/FreshRSS,Dolomich/FreshRSS,superboum/FreshRSS,FreshRSS/FreshRSS,marienfressinaud/FreshRSS,romibi/FreshRSS,romibi/FreshRSS,FreshRSS/FreshRSS,Alkarex/FreshRSS