Validate that timestamps are correct

There was a bug where timestamps could be in the future, which would make the zine show the same post every single day.

src/utilities.rs

@@ -26,13 +26,22 @@ pub fn read_feed(path: &str) -> Vec<Entry> {
         }
     }
 
-    // Remove any entries that don't have a timestamp, and then sort by timestamps
-    entries.retain(|entry| entry.published.is_some() || entry.updated.is_some());
+    entries.retain(validate_entry_date);
     entries.sort_by_key(|entry| Reverse(get_entry_date(entry)));
 
     entries
 }
 
+fn validate_entry_date(entry: &Entry) -> bool {
+    // Check that entry has a timestamp associated with it
+    if entry.published.is_some() || entry.updated.is_some() {
+        // Make sure post doesn't "exist in the future"
+        get_entry_date(entry) < chrono::Utc::now()
+    } else {
+        false
+    }
+}
+
 pub fn get_entry_date(entry: &Entry) -> chrono::DateTime<chrono::Utc> {
     entry.published.unwrap_or(entry.updated.unwrap_or_default())
 }