The ornamental design for a watchdial, as shown and described.
1. Watch dial
1.1 : Perspective
1.2 : Back
1.3 : Right
1.4 : Left
1.5 : Bottom
1.6 : Top
1.7 : Front
Representation 1.1 is a perspective view of the watch dial; representation 1.2 is a back view of the watch dial; representation 1.3 is a right side view of the watch dial; representation 1.4 is a left side view of the watch dial; representation 1.5 is a bottom view of the watch dial; representation 1.6 is a top view of the watch dial; representation 1.7 is a front view of the watch dial.