The ornamental design for an officechair, as shown and described.
FIG. 1 is a front elevational view of an office chair showing the claimed new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a left elevational view thereof;
FIG. 4 is a right elevational view thereof;
FIG. 5 is a top plane view thereof;
FIG. 6 is a bottom plane view thereof;
FIG. 7 is a front perspective view thereof; and,
FIG. 8 is a rear perspective view.
Any broken lines immediately adjacent to the claimed portions are boundaries, all other broken lines are environmental structures; all the broken lines form no part of the claimed design.