bug# 97770 fixing tree orange due to crash on unload

xpcom/components/nsComponentManager.cpp

@@ -1954,10 +1954,12 @@ nsComponentManagerImpl::UnloadLibraries(nsIServiceManager *serviceMgr, PRInt32 a
     /* iterate over all known loaders and ask them to autoregister. */
     // Skip mNativeComponentLoader
     for (int i=NS_COMPONENT_TYPE_NATIVE + 1; i<mNLoaderData; i++) {
+        if (mLoaderData[i].loader) {
             rv = mLoaderData[i].loader->UnloadAll(aWhen);
             if (NS_FAILED(rv))
                 break;
         }
+    }
 
     // UnloadAll the native loader
     rv = mNativeComponentLoader->UnloadAll(aWhen);