[search addon] Fix error on immediate search with no previous query
[search addon] Fix error on immediate search with no previous query

Searching with findPersistentNext or findPersistentPrev will
immediately run a search with the previous query, however it will throw
and error if no previous query exists. This commit fixes by preventing
the immediate execution if no previous query is set

jayaprabhakar/CodeMirror,jayaprabhakar/CodeMirror,INTELOGIE/CodeMirror,jkaplon/CodeMirror,codio/CodeMirror,SidPresse/CodeMirror,ejgallego/CodeMirror,alur/CodeMirror,jkaplon/CodeMirror,mtaran-google/CodeMirror,thomasjm/CodeMirror,sourcelair/CodeMirror,TDaglis/CodeMirror,pabloferz/CodeMirror,crazy4chrissi/CodeMirror,xeronith/CodeMirror,notepadqq/CodeMirror,alur/CodeMirror,adobe/CodeMirror2,nightwing/CodeMirror,grzegorzmazur/CodeMirror,pabloferz/CodeMirror,jkaplon/CodeMirror,sourcelair/CodeMirror,rrandom/CodeMirror,kerabromsmu/CodeMirror,ficristo/CodeMirror,ejgallego/CodeMirror,xeronith/CodeMirror,TDaglis/CodeMirror,nightwing/CodeMirror,wingify/CodeMirror,grzegorzmazur/CodeMirror,sourcelair/CodeMirror,dperetti/CodeMirror,INTELOGIE/CodeMirror,nightwing/CodeMirror,jayaprabhakar/CodeMirror,notepadqq/CodeMirror,xeronith/CodeMirror,mtaran-google/CodeMirror,hackmdio/CodeMirror,rrandom/CodeMirror,codio/CodeMirror,hackmdio/CodeMirror,notepadqq/CodeMirror,MarcelGerber/CodeMirror,rrandom/CodeMirror,INTELOGIE/CodeMirror,codio/CodeMirror,adobe/CodeMirror2,crazy4chrissi/CodeMirror,namin/CodeMirror,pabloferz/CodeMirror,MarcelGerber/CodeMirror,wingify/CodeMirror,ejgallego/CodeMirror,dperetti/CodeMirror,wingify/CodeMirror,grzegorzmazur/CodeMirror,kerabromsmu/CodeMirror,ficristo/CodeMirror,TDaglis/CodeMirror,thomasjm/CodeMirror,namin/CodeMirror,alur/CodeMirror,adobe/CodeMirror2,namin/CodeMirror,hackmdio/CodeMirror,SidPresse/CodeMirror,crazy4chrissi/CodeMirror,SidPresse/CodeMirror,schanzer/CodeMirror,thomasjm/CodeMirror,schanzer/CodeMirror,dperetti/CodeMirror,mtaran-google/CodeMirror,schanzer/CodeMirror,kerabromsmu/CodeMirror,MarcelGerber/CodeMirror,ficristo/CodeMirror