The ornamental design for a shower pan, as shown and described.
FIG. 1 is a top plan view showing a first embodiment of the new design. The bottom of the article is flat and devoid of surface ornamentation, and is therefore not shown.
FIG. 2 is a top left perspective view thereof; and,
FIG. 3 is an enlarged fragmentary view of a portion of the design.
The front, back, left and right side elevational views of the article are flat and devoid of surface ornamentation, and are therefore not shown.
The broken lines shown in the drawings represent unclaimed portions of the shower pan and forms no part of the claimed design.