The ornamental design for a curved shower bar, as shown and described.
FIG. 1 is a perspective view of a curved shower bar showing the new design;
FIG. 2 is a right side view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a front elevational view thereof;
FIG. 5 is a back view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a top view thereof.
The broken lines showing a handheld shower head and a shower head are for the purpose of illustrating environment and form no part of the claimed design.