Use first unread chapter for continue read buttons (#689)

src/lib/graphql/Fragments.ts

@@ -351,6 +351,9 @@ export const FULL_MANGA_FIELDS = gql`
         latestUploadedChapter {
             ...FULL_CHAPTER_FIELDS
         }
+        firstUnreadChapter {
+            ...FULL_CHAPTER_FIELDS
+        }
     }
 `;
 

src/lib/graphql/mutations/ChapterMutation.ts

@@ -113,6 +113,9 @@ export const UPDATE_CHAPTER = gql`
                     latestReadChapter {
                         id
                     }
+                    firstUnreadChapter {
+                        id
+                    }
                 }
             }
         }
@@ -156,6 +159,9 @@ export const UPDATE_CHAPTERS = gql`
                     latestReadChapter {
                         id
                     }
+                    firstUnreadChapter {
+                        id
+                    }
                 }
             }
         }