The ornamental design for a shutoffvalve, as shown and described.
FIG. 1 is a front-top perspective view of a shutoff valve showing my new design;
FIG. 2 is a front-bottom perspective view thereof;
FIG. 3 is a rear-top perspective view thereof;
FIG. 4 is a rear-bottom perspective view thereof;
FIG. 5 is a front elevational view thereof;
FIG. 6 is a rear elevational view thereof;
FIG. 7 is a left elevational view thereof;
FIG. 8 is a right elevational view thereof;
FIG. 9 is a top plan view thereof; and,
FIG. 10 is a bottom plan view thereof.
The broken lines shown in the figures are included for the purpose of illustrating portions of the shutoff valve and forms no part of the claimed design.