Fix errors detected after a first loading batch

After running a first batch of npm loading tasks, some errors were reported [1] Let's fix them before scheduling a new batch.

• [1] http://kibana0.internal.softwareheritage.org:5601/app/kibana#/dashboard/07631b40-5c52-11e9-b8ce-cf95f437ce37?_g=(refreshInterval:(pause:!t,value:0),time:(from:now-12h,mode:quick,to:now))&_a=(description:'',filters:!(('state':(store:appState),meta:(alias:!n,disabled:!f,index:'20de3150-c0bb-11e8-8222-07f3ec376cd5',key:priority,negate:!f,params:(query:'3',type:phrase),type:phrase,value:'3'),query:(match:(priority:(query:'3',type:phrase)))),('state':(store:appState),meta:(alias:!n,disabled:!f,index:'20de3150-c0bb-11e8-8222-07f3ec376cd5',key:message,negate:!t,params:(query:'swh.storage.HashCollision:+sha1',type:phrase),type:phrase,value:'swh.storage.HashCollision:+sha1'),query:(match:(message:(query:'swh.storage.HashCollision:+sha1',type:phrase))))),fullScreenMode:!f,options:(darkTheme:!t,hidePanelTitles:!f,useMargins:!f),panels:!((embeddableConfig:(),gridData:(h:44,i:'1',w:47,x:0,y:0),id:'4167d160-5c51-11e9-b8ce-cf95f437ce37',panelIndex:'1',type:search,version:'6.4.2')),query:(language:kuery,query:''),timeRestore:!t,title:swh-loader-npm,viewMode:view)

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Migrated from T1644 (view on Phabricator)