AP_Compass: ignore COMPASS_ORIENT for internal compass

this means if COMPASS_ORIENT is not 0 and the external compass fails
to start on boot we don't end up with a bad compass orientation

libraries/AP_Compass/AP_Compass_PX4.cpp

@@ -89,13 +89,13 @@ bool AP_Compass_PX4::read(void)
     // a noop on most boards
     _sum.rotate(MAG_BOARD_ORIENTATION);
 
-    // add user selectable orientation
-    _sum.rotate((enum Rotation)_orientation.get());
-
     // override any user setting of COMPASS_EXTERNAL 
     _external.set(_is_external);
 
-    if (!_external) {
+    if (_external) {
+        // add user selectable orientation
+        _sum.rotate((enum Rotation)_orientation.get());
+    } else {
         // add in board orientation from AHRS
         _sum.rotate(_board_orientation);
     }