EXT-6527 FIXED Avoided show agent/group SLURL icon in plain text mode.

reviewed by Richard Nelson at https://codereview.productengine.com/secondlife/r/773/

--HG--
branch : product-engine

indra/newview/llappviewer.cpp

@@ -357,7 +357,7 @@ static void ui_audio_callback(const LLUUID& uuid)
 
 bool	create_text_segment_icon_from_url_match(LLUrlMatch* match,LLTextBase* base)
 {
-	if(!match || !base)
+	if(!match || !base || base->getPlainText())
 		return false;
 
 	LLUUID match_id = match->getID();