The ornamental design for an inflatableblanket, as shown and described.
FIG. 1 is a perspective view showing the new design for an inflatable blanket.
FIG. 2 is a top plane view thereof;
FIG. 3 is a bottom plane view thereof;
FIG. 4 is a left side view, the opposite side being a mirror image thereof; and,
FIG. 5 is a front end view, the opposite end being a mirror image thereof.
The portions of the inflatable blanket in FIGS. 1-5 shown in broken lines are included to show features that form no part of the claimed design. In addition, the dot-dash-dot type broken lines shown in the drawing views define the boundaries of the claimed design and form no part of the claimed design.