Fix inability to unblock an abandoned claim

The recent change to parse the channel from a Repost using a `claim` ended up breaking the case for abandoned claims, which `claim` will be `null`.

Fix by looking at `claim` first (faster), and falling back to the `parseURI` method if it remains inconclusive.

ui/component/claimPreview/view.jsx

@@ -7,6 +7,7 @@ import { lazyImport } from 'util/lazyImport';
 import classnames from 'classnames';
 import { isURIValid } from 'util/lbryURI';
 import * as COLLECTIONS_CONSTS from 'constants/collections';
+import { isChannelClaim } from 'util/claim';
 import { formatLbryUrlForWeb } from 'util/url';
 import { formatClaimPreviewTitle } from 'util/formatAriaLabel';
 import FileThumbnail from 'component/fileThumbnail';
@@ -180,7 +181,7 @@ const ClaimPreview = forwardRef<any, {}>((props: Props, ref: any) => {
     claim.value.stream_type &&
     // $FlowFixMe
     (claim.value.stream_type === 'audio' || claim.value.stream_type === 'video');
-  const isChannelUri = claim ? claim.value_type === 'channel' : false;
+  const isChannelUri = isChannelClaim(claim, uri);
   const signingChannel = claim && claim.signing_channel;
   const repostedChannelUri =
     claim && claim.repost_channel_url && claim.value_type === 'channel'

ui/util/claim.js

@@ -1,5 +1,6 @@
 // @flow
 import { MATURE_TAGS } from 'constants/tags';
+import { parseURI } from 'util/lbryURI';
 
 const matureTagMap = MATURE_TAGS.reduce((acc, tag) => ({ ...acc, [tag]: true }), {});
 
@@ -66,6 +67,28 @@ export function filterClaims(claims: Array<Claim>, query: ?string): Array<Claim>
   return claims;
 }
 
+/**
+ * Determines if the claim is a channel.
+ *
+ * @param claim
+ * @param uri An abandoned claim will be null, so provide the `uri` as a fallback to parse.
+ */
+export function isChannelClaim(claim: ?Claim, uri?: string) {
+  // 1. parseURI can't resolve a repost's channel, so a `claim` will be needed.
+  // 2. parseURI is still needed to cover the case of abandoned claims.
+  if (claim) {
+    return claim.value_type === 'channel';
+  } else if (uri) {
+    try {
+      return Boolean(parseURI(uri).isChannel);
+    } catch (err) {
+      return false;
+    }
+  } else {
+    return false;
+  }
+}
+
 export function getChannelIdFromClaim(claim: ?Claim) {
   if (claim) {
     if (claim.value_type === 'channel') {