The ornamental design for a flowcontroller, as shown and described.
FIG. 1 is a rear perspective view of a flow controller according to our design;
FIG. 2 is a reverse perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a right side view thereof; and,
FIG. 6 is a bottom view thereof.
Throughout the various figures of the drawings, certain views may not be provided. The omission of a particular view is intended to convey that the element(s) depicted is/are plain and unornamented in that omitted view, that the omitted view is similar to other views, or that the particular ornamental appearance in that view is simply not claimed.