Fixes for URL echo Apple Event handling from Steve Cox <scox@artlogic.com> for bug 44250. r=smfr

xpfe/bootstrap/appleevents/nsAEUtils.cpp

@@ -91,13 +91,17 @@ exit:
 
 OSErr AEGetDescData(const AEDesc *theAEDesc, void *dataPtr, Size maximumSize)
 {
+  OSErr err = noErr;
+  
 	if (theAEDesc->dataHandle)
 	{
 		Size dataLength = GetHandleSize(theAEDesc->dataHandle);
 		BlockMoveData(*theAEDesc->dataHandle, dataPtr, Min(dataLength, maximumSize));
 	}
 	else
-		return paramErr;
+		err = paramErr;
+		
+	return err;
 }
 
 /*----------------------------------------------------------------------------

xpfe/bootstrap/nsDocLoadObserver.cpp

@@ -80,6 +80,9 @@ void nsDocLoadObserver::Unregister()
 
 void nsDocLoadObserver::AddEchoRequester(OSType appSignature)
 {
+  // make sure an application is only in the list once
+  mEchoRequesters.RemoveElement((void*)appSignature);
+  
 	mEchoRequesters.AppendElement((void*)appSignature);
 	Register();     // ensure we are registered
 }