Bug 1594730 - fix silly bug for the background event target; r=KrisWright

The static analysis caught this for me in Bug 1593812, I was just to
dumb to actually apply this change prior to commit.

Differential Revision: https://phabricator.services.mozilla.com/D52170

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

xpcom/threads/nsThreadManager.cpp

@@ -109,7 +109,7 @@ BackgroundEventTarget::IsOnCurrentThreadInfallible() {
 NS_IMETHODIMP
 BackgroundEventTarget::IsOnCurrentThread(bool* aValue) {
   bool value = false;
-  if (NS_SUCCEEDED(mPool->IsOnCurrentThread(aValue)) && value) {
+  if (NS_SUCCEEDED(mPool->IsOnCurrentThread(&value)) && value) {
     *aValue = value;
     return NS_OK;
   }