Fix bug reporting HMD when we shouldn't be.

This boils down to: Detection occurs in two phases,
and I only stopped one of the phases from looking at the HMD.

Alternative fix could have been to prevent the second phase from
adding trackers to the current set, but eh.

src/main.cpp

@@ -519,6 +519,10 @@ class Trackers {
 		}
 
 		for (unsigned int jjj = 0; jjj < (int)BodyPosition::BodyPosition_Count; ++jjj) {
+			if (!enable_hmd && jjj == (int)BodyPosition::Head) {
+				continue; // don't query the head if we aren't reporting it.
+			}
+
 			InputPoseActionData_t pose;
 			input_error = input->GetPoseActionDataRelativeToNow(action_handles[jjj], universe, 0, &pose, sizeof(pose), 0);
 			if (input_error != EVRInputError::VRInputError_None) {