Take care of reviewer comment (bug 373219).

xpcom/base/nsCycleCollector.cpp

@@ -1532,7 +1532,7 @@ nsCycleCollector::Suspect(nsISupports *n)
     if (!NS_IsMainThread())
         Fault("trying to suspect from non-main thread");
 
-    if (!n || !nsCycleCollector_isScanSafe(n))
+    if (!nsCycleCollector_isScanSafe(n))
         Fault("suspected a non-scansafe pointer", n);    
 
     if (nsCycleCollector_shouldSuppress(n))
@@ -1764,6 +1764,9 @@ nsCycleCollector_isScanSafe(nsISupports *s)
 {
     nsresult rv;
 
+    if (!s)
+        return PR_FALSE;
+
     nsCOMPtr<nsCycleCollectionParticipant> cp = do_QueryInterface(s, &rv);
     if (NS_FAILED(rv)) {
         sCollector.mStats.mFailedQI++;