WEB-1819 PARTIAL follow-up tweak.

this makes a new externally-invoked search blank-out the old search
until it starts really loading.

indra/newview/llfloatersearch.cpp

@@ -115,6 +115,10 @@ void LLFloaterSearch::onOpen(const LLSD& key)
 {
 	if ( (key.has("category")) || ((mBrowser) && (mBrowser->getCurrentNavUrl().empty())) )
 	{
+		// new search triggered - blank the page while loading, instead of
+		//  temporarily showing stale results
+		mBrowser->navigateTo("about:blank");
+
 		search(key);
 	}
 }