cave/activitypub: ignore more weird tags

cave/src/activitypub/mod.rs

@@ -118,12 +118,16 @@ impl Post {
                 while tag.name.chars().next() == Some('#') {
                     tag.name.remove(0);
                 }
-                if tag.name.chars().next() == Some('@') {
+                if let Some(c) = tag.name.chars().next() {
-                    // why do these occur?
+                    // check the first letter
-                    None
+                    if ['@', ':'].contains(&c) {
-                } else if tag.name.len() > 0 {
+                        // these are weird
-                    Some(tag)
+                        None
+                    } else {
+                        Some(tag)
+                    }
                 } else {
+                    // no first letter
                     None
                 }
             }).collect(),