middle click viewport jump

*ArmorPaint 1.0-1e74163, Windows*

**Issue description:**
clicking with middle click on the mesh makes the viewport jump.

**Steps to reproduce:**
open armorpaint, middle click with the cursor on the mesh.

Thanks

Reproduce the issue in ArmorPaint 1.0-1e74163 on Windows by opening the app and middle-clicking with the cursor on the mesh. Then trace the middle-click viewport input handling; the work is done when this interaction no longer makes the viewport jump.

Written by the indexing model from the issue text.