IM: defensive fix to get rid of warnings about attempts to get speaker mgr for removed sessions

--HG--
branch : product-engine

indra/newview/llimfloater.cpp

@@ -106,6 +106,8 @@ void LLIMFloater::onFocusReceived()
 // virtual
 void LLIMFloater::onClose(bool app_quitting)
 {
+	if (!gIMMgr->hasSession(mSessionID)) return;
+	
 	setTyping(false);
 	gIMMgr->leaveSession(mSessionID);
 }