AP_Common: avoid using AP_Math is_zero() because it is classless

- because it is classless it can not be called like AP_Math::is_zero() and will then conflict with local definition of is_zero()

libraries/AP_Common/Location.cpp

@@ -234,7 +234,8 @@ float Location_Class::get_distance(const struct Location &loc2) const
 // extrapolate latitude/longitude given distances (in meters) north and east
 void Location_Class::offset(float ofs_north, float ofs_east)
 {
-    if (!is_zero(ofs_north) || !is_zero(ofs_east)) {
+    // use is_equal() because is_zero() is a local class conflict and is_zero() in AP_Math does not belong to a class
+    if (!is_equal(ofs_north, 0.0f) || !is_equal(ofs_east, 0.0f)) {
         int32_t dlat = ofs_north * LOCATION_SCALING_FACTOR_INV;
         int32_t dlng = (ofs_east * LOCATION_SCALING_FACTOR_INV) / longitude_scale(*this);
         lat += dlat;