workaroung a warning for const that prevents gtk1 builds

svn path=/trunk/; revision=21850

wiretap/wtap-plugins.c

@@ -94,13 +94,14 @@ void wtap_load_plugins(char* dirname) {
 		lt_lib_ext = strrchr(hack_path, '.');
 		if (lt_lib_ext == NULL)
 		{
+			gchar null_str[1] = {0};
 			/*
 			 * Does this mean there *is* no extension?  Assume so.
 			 *
 			 * XXX - the code below assumes that all loadable modules have
 			 * an extension....
 			 */
-			lt_lib_ext = "";
+			lt_lib_ext = null_str;
 		}
 #endif