EXT-7591 FIX Typing the first characters of a selection in a dropdown will ignore the first letter

clear the searchstring on list focus lost, not setFocus, so that the act of popping open the list when you type the first letter doesn't clear the first letter from the search string

indra/llui/llscrolllistctrl.cpp

@@ -2949,7 +2949,6 @@ BOOL LLScrollListCtrl::operateOnAll(EOperation op)
 //virtual 
 void LLScrollListCtrl::setFocus(BOOL b)
 {
-	mSearchString.clear();
 	// for tabbing into pristine scroll lists (Finder)
 	if (!getFirstSelected())
 	{
@@ -2994,6 +2993,9 @@ void LLScrollListCtrl::onFocusLost()
 	{
 		gFocusMgr.setMouseCapture(NULL);
 	}
+
+	mSearchString.clear();
+
 	LLUICtrl::onFocusLost();
 }