extensive orb_advert_t fixes

The calls to orb_advertise were being mishandled throughout the code.
There were ::close() calls on memory pointers, there were checks
against < 0 when it is a pointer to a object and values larger than
0x7ffffffff are valid. Some places orb_advert_t variables were
being initialized as 0 other places as -1.

The orb_advert_t type was changed to uintptr_t so the pointer value
would not be wrapped as a negative number. This was causing a failure
on ARM.

Tests for < 0 were changed to == 0 since a null pointer is the valid
representation for error, or uninitialized.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/drivers/gimbal/gimbal.cpp

@@ -180,7 +180,7 @@ Gimbal::Gimbal() :
 	_attitude_compensation_pitch(true),
 	_attitude_compensation_yaw(true),
 	_initialized(false),
-	_actuator_controls_2_topic(-1),
+	_actuator_controls_2_topic(0),
 	_sample_perf(perf_alloc(PC_ELAPSED, "gimbal_read")),
 	_comms_errors(perf_alloc(PC_COUNT, "gimbal_comms_errors")),
 	_buffer_overflows(perf_alloc(PC_COUNT, "gimbal_buffer_overflows"))
@@ -197,7 +197,6 @@ Gimbal::~Gimbal()
 	/* make sure we are truly inactive */
 	stop();
 
-	::close(_actuator_controls_2_topic);
 	::close(_vehicle_command_sub);
 }
 
@@ -281,7 +280,7 @@ Gimbal::cycle()
 		zero_report.timestamp = hrt_absolute_time();
 		_actuator_controls_2_topic = orb_advertise(ORB_ID(actuator_controls_2), &zero_report);
 
-		if (_actuator_controls_2_topic < 0) {
+		if (_actuator_controls_2_topic == 0) {
 			warnx("advert err");
 		}