Bug 1547871 - BrowsingContext needs a group to evict from cache. r=neha

Differential Revision: https://phabricator.services.mozilla.com/D29669

--HG--
extra : moz-landing-system : lando

docshell/base/BrowsingContext.cpp

@@ -283,7 +283,7 @@ void BrowsingContext::Detach(bool aFromIPC) {
 
   RefPtr<BrowsingContext> kungFuDeathGrip(this);
 
-  if (!Group()->EvictCachedContext(this)) {
+  if (Group() && !Group()->EvictCachedContext(this)) {
     Children* children = nullptr;
     if (mParent) {
       children = &mParent->mChildren;