Ignore touch collections that carry no coordinate data

[mhrpii]

Problem

On a Waveshare 10.4" QLED capacitive touchscreen (VID 0x0712, PID 0x000A,
10-point HID digitizer), every finger lift spawns a phantom touch at a bogus
screen position. The phantom is visible in the debug overlay and lingers for the
0.5 s deferred-removal window. Rapid successive strokes accumulate several at
once.

Root cause

The panel reports ContactCount = 10 in its lift-off report instead of 0:

64 | 0xd (Dig) | 0x54 (ContCnt) |  10
63 | 0xd (Dig) | 0x56 (ScnTime) |  27542
23 | 0xd (Dig) | 0x42 (Tip)     |   0

DispatchTouches() trusts that count and dispatches all ten collections.
Collections 1–9 never received any values in this report, so
DispatchTouchDataForCollection() leaves x and y at their -1 sentinel and
still calls TouchInputManagerUpdateTouchPosition(). Each of those nine calls
creates or revives a touch at a meaningless location.

Two details make it worse on this device: it never transmits
ContactIdentifier at all, so every collection resolves to contact ID 0; and
ignoreOriginTouches cannot help, since it tests for exact CGPointZero and the
sentinel is (-1, -1).

The kernel-side view is clean — evtest on Linux shows a correct
ABS_MT_TRACKING_ID: -1 on release — so this is purely about how the raw HID
report is interpreted.

Fix

Bail out of DispatchTouchDataForCollection() when the collection produced no
coordinate values. A collection with no X/Y data should never produce a touch,
regardless of what ContactCount claims.

Testing

Verified on macOS Tahoe with the panel above: phantom touches are gone, and
normal tracking, tapping, dragging and scrolling are unaffected.