Strange behaviour with Steam window

**Describe the bug**
The drop-down interface that appears only when you drag a window also appears when you click on the top part of the Steam window.

**To Reproduce**
Steps to reproduce the behavior:
1. Open Steam
2. Click (and hold click) on top part of the window
3. Then the layouts show without moving the window

**Screenshots**

**Information (please complete the following):**
- Tiling Shell version: 17.3
- GNOME version: 48.7.

Start by reproducing the issue with Steam on GNOME 48.7 using Tiling Shell 17.3: hold the click on the window’s top area without moving it and observe whether the layouts appear. Trace the window-drag and click handling, then verify that layouts appear only after an actual drag and that normal Steam window clicks remain unaffected.

Written by the indexing model from the issue text.