The ornamental design for a handheld shower, as shown and described.
FIG. 1 is a perspective view of a handheld shower showing our new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a front elevational view thereof; and,
FIG. 7 is a rear view thereof.
The broken line showing of the front portion of the shower head is included for the purpose of illustrating environment and forms no part of the claimed design.