fix: price data update time serialization

price update time was not properly serialized as a number like the schema was, and led to dates being stored as empty objects. UI code also did not check if date was NaN, and rendered "invalid date" instead.

src/content/content.ts

@@ -250,7 +250,7 @@ async function inject() {
 		}).reverse().forEach((element) => {
 			priceInfoboxHeadingRow.insertAdjacentElement('afterend', element.row);
 		})
-		if(!updateTime) { updateTime = new Date() }
+		if(!updateTime || !(updateTime instanceof Date) || isNaN(+updateTime)) updateTime = new Date()
 
 		// Footer row
 		const row = document.createElement("tr");