Reproduction steps:
1. Open the attached project "BugReport_LockMouse_RepositionsWindow.zip";
2. Select File -> Build & Run;
3. As soon as the window shows up, slightly move the window around;

Expected results: Dragging the window while modifying Cursor.lockState should not screw the window position.
Actual results: Once the splash-screen completed, the window is positioned outside the screen and cannot be brought back.

Reproduced on: 5.6.1p1, 5.6.2p4, 2017.1.0f3, 2017.2.0b4, 2017.3.0a1.
Not reproduced on: 5.5.3p3.
Regression first introduced: 5.6.1p1.