ECPG: Simplify free_variable()

Patch by Boszormenyi Zoltan <zb@cybertec.at>

src/interfaces/ecpg/ecpglib/execute.c

@@ -87,16 +87,11 @@ free_variable(struct variable * var)
 {
 	struct variable *var_next;
 
-	if (var == NULL)
-		return;
-	var_next = var->next;
-	ecpg_free(var);
-
-	while (var_next)
+	while (var)
 	{
-		var = var_next;
 		var_next = var->next;
 		ecpg_free(var);
+		var = var_next;
 	}
 }