The ornamental design for a nebulizer, as shown and described.
FIG. 1 is a perspective view of a nebulizer;
FIG. 2 is a front view thereof;
FIG. 3 is a left side view thereof, the right side view being a mirror image thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a top elevation view thereof;
FIG. 6 is a bottom elevation view thereof;
FIG. 7 is a perspective view of the nebulizer;
FIG. 8 is a front view of the nebulizer;
FIG. 9 is a left side view of the nebulizer;
FIG. 10 is a rear view of the nebulizer; and,
FIG. 11 is a top elevation view of the nebulizer.
The broken line showing on the bottom of the article is included for the purpose of illustrating environmental structure and forms no part of the claimed design.