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/hott/messages.cpp

@@ -63,7 +63,7 @@ static int _sensor_sub = -1;
 static int _airspeed_sub = -1;
 static int _esc_sub = -1;
 
-static orb_advert_t _esc_pub;
+static orb_advert_t _esc_pub = 0;
 
 static bool _home_position_set = false;
 static double _home_lat = 0.0d;