fix filename generation

frontend/src/components/canvas/Canvas.vue

@@ -41,10 +41,16 @@ export default {
 
       let link = document.createElement("a");
 
-      if (window.fileName !== undefined) {
+      if (
+        window.fileName !== undefined && window.fileName !== null
+        && (typeof window.fileName === 'string' || window.fileName instanceof String)
+        && window.fileName.length >= 1
+      ) {
         link.download = window.fileName;
       } else {
-        link.download = `Generator-${new Date().toLocaleString()}.png`;
+        const date = new Date().toLocaleString();
+
+        link.download = `Generator-${date}.png`;
       }
 
       link.href = this.$refs.canvas.toDataURL();