The ornamental design for an inhaler, as shown and described.
1.1 : Right
1.2 : Left
1.3 : Front
1.4 : Back
1.5 : Top
1.6 : Bottom
1.7 : Perspective
The dash-dash broken lines represent portions of the inhaler and form no part of the claimed design. The dash-dot broken lines represent a boundary between claimed and unclaimed subject matter and form no part of the claimed design.