The ornamental design for a candle warmer, as shown and described.
FIG. 1 is a rear perspective view thereof;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a right elevation view thereof, with the left elevation view being substantially the same;
FIG. 5 is a top plan thereof; and,
FIG. 6 is a bottom plan thereof.
The electric cord and cord opening on the rear side of the candle warmer are shown in broken lines and form no part of the claimed design. The broken lines immediately adjacent to the shaded areas in FIG. 5 represent the bounds of the claimed design and form no part thereof.