The ornamental design for a carrier, as shown and described.
FIG. 1 is a front view of a first embodiment of our design; and,
FIG. 2 is a front view of a second embodiment of our design.
The dot-dash broken lines represent the metes and bounds of the claim and form no part of the claimed design. The broken lines showing the snowflakes are for the purposes of illustrating environment and form no part of the claimed design.