Merge branch 'diff-js-error-fix' into 'master'

Fixed issue with spinner not hiding on diff changes

See merge request !3793

app/assets/javascripts/merge_request_tabs.js.coffee

@@ -183,6 +183,7 @@ class @MergeRequestTabs
       else
         $diffLine = $('td', $diffLine)
 
+      if $diffLine.length
         $diffLine.addClass 'hll'
         diffLineTop = $diffLine.offset().top
         navBarHeight = $('.navbar-gitlab').outerHeight()