Plane: fixed bug in pullup code

if we have poor pitch trim it is possible we will pullup before
reaching the target airspeed. Check pitch threshold during airspeed
stage of pullup

ArduPlane/pullup.cpp

@@ -115,7 +115,7 @@ bool GliderPullup::verify_pullup(void)
     switch (stage) {
     case Stage::WAIT_AIRSPEED: {
         float aspeed;
-        if (ahrs.airspeed_estimate(aspeed) && aspeed > airspeed_start) {
+        if (ahrs.airspeed_estimate(aspeed) && (aspeed > airspeed_start || ahrs.pitch_sensor*0.01 > pitch_start)) {
             gcs().send_text(MAV_SEVERITY_INFO, "Pullup airspeed %.1fm/s alt %.1fm AMSL", aspeed, current_loc.alt*0.01);
             stage = Stage::WAIT_PITCH;
         }