The ornamental design for a heatingstove, as shown and described.
FIG. 1 is a front view of a heating stove showing our new design;
FIG. 2 is a back view of the heating stove of FIG. 1;
FIG. 3 is a left side view of the heating stove;
FIG. 4 is a right side view of the heating stove;
FIG. 5 is a top view of the heating stove; and,
FIG. 6 is an upward view of the heating stove.
The cut away portions in the drawings indicate the appearance of any portion of the article between the cut away lines forms no part of the claimed design.