Fix usage of LLResMgr::getIntegerString with same output string multiple times

indra/llui/llresmgr.cpp

@@ -254,6 +254,7 @@ void LLResMgr::getIntegerString( std::string& output, S32 input ) const
 	}
 	
 	// *NOTE: this method does not handle negative input integers correctly
+	output.clear();
 	S32 fraction = 0;
 	std::string fraction_string;
 	S32 remaining_count = input;