The ornamental design for a flowregulator, as shown and described.
FIG. 1 is a top perspective view of a flow regulator showing my new design;
FIG. 2 is an elevational view thereof;
FIG. 3 is a top plan view thereof; and,
FIG. 4 is a bottom plan view thereof, wherein the dashed lines show environmental matter for illustrative purposes only and do not form part of the claimed design.