I claim the ornamental design for a manual dough cutter, as shown and described.
FIG. 1 is a top perspective view of a manual dough cutter showing my new design;
FIG. 2 is a front view thereof, the back view being substantially the same;
FIG. 3 is a right side view thereof, the left side view being substantially the same;
FIG. 4 is a top view thereof; and,
FIG. 5 is a bottom view thereof.
Material shown in the several views in broken lines illustrates variable environmental material and should not be considered part of the claimed design.