[NTUSER] Fix sticky mouse buttons (#6426)

[NTUSER] Fix sticky mouse buttons (#6426)

Fix Mouse Buttons Sticking Down causing unexpected window dragging.
This is a patch supplied by @I_Kill_Bugs and seems to work well as tested by @julenuri.

JIRA issue: CORE-11775 'GIMP 2.6.12: Sticky issue when dragging with the mouse'
JIRA issue: CORE-14998 'Google Chrome 40.0.2214.115, when moving window position by dragging at the titlebar, the drag-end is not detected, the window may stick with the mouse pointer'
Improves JIRA issue: CORE-18511

Proposed changes
Add extra code into nonclient.c procedure DefWndDoSizeMove to drop tracking.
If we get a mouse move with the mouse left button down, then break out of testing.