Copter: enable ekf_check only after ekf origin has been set

ArduCopter/ekf_check.cpp

@@ -30,6 +30,12 @@ static struct {
 // should be called at 10hz
 void Copter::ekf_check()
 {
+    // exit immediately if ekf has no origin yet - this assumes the origin can never become unset
+    Location temp_loc;
+    if (!ahrs.get_NavEKF_const().getOriginLLH(temp_loc)) {
+        return;
+    }
+
     // return immediately if motors are not armed, ekf check is disabled, not using ekf or usb is connected
     if (!motors.armed() || ap.usb_connected || (g.fs_ekf_thresh <= 0.0f)) {
         ekf_check_state.fail_count = 0;