fix for SH-2559: [crashhunters] crash in LLPluginMessage::generate()

discussed and reviewed by callum.

indra/newview/llviewermedia.cpp

@@ -2450,10 +2450,24 @@ BOOL LLViewerMediaImpl::handleMouseUp(S32 x, S32 y, MASK mask)
 //////////////////////////////////////////////////////////////////////////////////////////
 void LLViewerMediaImpl::updateJavascriptObject()
 {
+	static LLFrameTimer timer ;
+
 	if ( mMediaSource )
 	{
 		// flag to expose this information to internal browser or not.
 		bool enable = gSavedSettings.getBOOL("BrowserEnableJSObject");
+
+		if(!enable)
+		{
+			return ; //no need to go further.
+		}
+
+		if(timer.getElapsedTimeF32() < 1.0f)
+		{
+			return ; //do not update more than once per second.
+		}
+		timer.reset() ;
+
 		mMediaSource->jsEnableObject( enable );
 
 		// these values are only menaingful after login so don't set them before