Improve not found error handling for the covert art client;

Author: Haschikeks

lib/coverartarchive-api.ts

@@ -37,7 +37,23 @@ export class CoverArtArchiveApi {
         Accept: "application/json"
       }
     });
-    return response.json();
+
+    try {
+      const j = await response.json();
+      return j;
+    } catch (e) {
+      if (response.status === 404) {
+        return {
+            "error": "Not Found",
+            "help": "For usage, please see: https://musicbrainz.org/development/mmd"
+        }
+      } else {
+        return {
+          "error": (e as Error).message,
+          "help": "For usage, please see: https://musicbrainz.org/development/mmd"
+        }
+      }
+    }
   }
 
   /**