The ornamental design for an officechair, as shown and described.
FIG. 1 is a front view of the office chair showing my new design;
FIG. 2 is a back view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a perspective view thereof.
The dotted dashes lines shown on the backrest represent fabric and the other broken lines shown in the drawing are for illustrating environmental structure. All the dotted dash lines and broken lines form no party of the claimed design.