The ornamental design for a head-mounted display device, as shown and described.
1. Head-mounted display device
1.1 : Front
1.2 : Back
1.3 : Left
1.4 : Right
1.5 : Top
1.6 : Bottom
1.7 : Perspective
The broken lines are included for the purpose of illustrating portions of the head-mounted display device that form no part of the claimed design.
Reproduction 1.1 is a front elevation view of a head-mounted display device showing our new design; reproduction 1.2 is a rear elevation view thereof; reproduction 1.3 is a left side elevation view thereof; reproduction 1.4 is a right side elevation view thereof; reproduction 1.5 is a top plan view thereof; reproduction 1.6 is a bottom plan view thereof; and reproduction 1.7 is a perspective view thereof, the human body in grey as shown in reproduction 1.7 does not form a part of the claimed product.