fix PieceTable::Cursor::next_line()

src/core/PieceTable.cc

@@ -285,12 +285,7 @@ PieceTable::Piece * PieceTable::Cursor::next_line() const
     {
         return nullptr;
     }
-    p = p->next;
-    while ((!p->eol()) && (p->next != iterator.piece_table->end_piece))
-    {
-        p = p->next;
-    }
-    return p;
+    return p->next;
 }
 
 void PieceTable::Cursor::init_column()