The ornamental design for a fireplace, as shown and described.
FIG. 1 is a front perspective view of a fireplace showing my new and original design;
FIG. 2 is a front view elevation thereof;
FIG. 3 is a right side elevation view thereof; and,
FIG. 4 is a left side elevation view thereof.
The rear, top, and bottom sides of the design form no part of the claimed design. The broken lines and the area within the broken lines represent environmental subject matter and form no part of the claimed design.