Copter: check fence when disarmed

this allows catching fence breaches as part of arming checks

ArduCopter/fence.cpp

@@ -13,17 +13,17 @@ void Copter::fence_check()
     uint8_t new_breaches; // the type of fence that has been breached
     uint8_t orig_breaches = fence.get_breaches();
 
-    // return immediately if motors are not armed
-    if(!motors.armed()) {
-        return;
-    }
-
     // give fence library our current distance from home in meters
     fence.set_home_distance(home_distance*0.01f);
 
     // check for a breach
     new_breaches = fence.check_fence(current_loc.alt/100.0f);
 
+    // return immediately if motors are not armed
+    if(!motors.armed()) {
+        return;
+    }
+
     // if there is a new breach take action
     if( new_breaches != AC_FENCE_TYPE_NONE ) {