Fix default filename logic

mods/save_loading.js

@@ -58,6 +58,9 @@ function formatCurrentDate() { //derived from https://gist.github.com/Ivlyth/c49
 function savePrompt() {
 	var filename = prompt("Please enter the desired filename, without the .json (defaults to current date)");
 	if(filename === null) {
+		return false;
+        };
+        if(filename === "") {
             filename = `Sandboxels save ${formatCurrentDate()}`;
 	};
 	filename += ".json";