[PicoXR] Do not disable controllers when disabling hand tracking

The PicoXR runtime is a bit special with regard to controller tracking.
It never stops tracking them even if the controller was left aside or
is outside users' field of view. That's why the PicoXR runtime
considers the controllers as always available. We usually use that
availability to decide whether to render hands or controllers.

For the case of PicoXR, as controllers always appear as available,
we have to always check for hand tracking. The problem is that
it was not properly done. In the case of having hand tracking
disabled the code was disabling all controllers. The problem was
that, in order to force a hand tracking check, we were forcing
the variable that checked whether or not controllers were available
to false. If hand tracking was disabled by users, then the code
was disabling all controllers, because hand tracking was not
available and there were no controllers.

We should instead use a different variable to force the hand
tracking check without overwritting other variables which cause
nasty side effects like this one.

Fixes Igalia#1721

app/src/openxr/cpp/OpenXRInputSource.cpp

@@ -795,17 +795,17 @@ void OpenXRInputSource::Update(const XrFrameState& frameState, XrSpace localSpac
         return;
     }
 
+    bool isControllerUnavailable = (poseLocation.locationFlags & XR_SPACE_LOCATION_ORIENTATION_VALID_BIT) == 0;
+    auto gotHandTrackingInfo = false;
+    auto handFacesHead = false;
 #if defined(PICOXR)
     // Pico does continuously track the controllers even when left alone. That's why we return
-    // always true so that we always check hand tracking just in case.
-    bool isControllerUnavailable = true;
+    // always true so that we always check hand tracking just in case (unless it's disabled).
+    bool mustAlwaysCheckHandTracking = handTrackingEnabled;
 #else
-    bool isControllerUnavailable = (poseLocation.locationFlags & XR_SPACE_LOCATION_ORIENTATION_VALID_BIT) == 0;
+    bool mustAlwaysCheckHandTracking = false;
 #endif
-
-    auto gotHandTrackingInfo = false;
-    auto handFacesHead = false;
-    if (isControllerUnavailable || mUsingHandInteractionProfile) {
+    if (isControllerUnavailable || mUsingHandInteractionProfile || mustAlwaysCheckHandTracking) {
         if (!handTrackingEnabled) {
             delegate.SetEnabled(mIndex, false);
             return;