The ornamental design for a candlestick, as shown and described.
FIG. 1 is a view in elevation of a candlestick in accordance with the
claimed design, where the same appearance is presented when looking at the
candlestick from any direction;
FIG. 2 is a top plan view of the claimed design; and,
FIG. 3 is a bottom plan view of the claimed design.
The candle is shown in broken lines for illustrative purposes only.