cave: fix #tags in Post.to_feed_post()

cave/src/activitypub/mod.rs

@@ -112,7 +112,16 @@ impl Post {
                 url: actor.url.unwrap_or(actor.id),
                 bot: actor.actor_type != "Person",
             },
-            tags: self.tag,
+            tags: self.tag.into_iter().filter_map(|mut tag| {
+                while tag.name.chars().next() == Some('#') {
+                    tag.name.remove(0);
+                }
+                if tag.name.len() > 0 {
+                    Some(tag)
+                } else {
+                    None
+                }
+            }).collect(),
             sensitive: self.sensitive,
             mentions: vec![],
             language,