The ornamental design for a fireplace, as shown and described.
FIG. 1 is a front perspective view for a fireplace showing my new and original design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a right side elevation view thereof; and,
FIG. 4 is a left side elevation view thereof.
The bottom and rear are not included in the claim. The broken lines and the area within the broken lines represent environmental subject matter that forms no part of the claimed design.