Replay: cope with bad NSats field from old logs

Tools/Replay/LR_MsgHandler.cpp

@@ -154,12 +154,17 @@ void LR_MsgHandler_GPS_Base::update_from_msg_gps(uint8_t gps_offset, uint8_t *ms
         ! field_value(msg, "HDp", hdop)) {
         hdop = 20;
     }
+    uint8_t nsats = 0;
+    if (! field_value(msg, "NSats", nsats) &&
+        ! field_value(msg, "numSV", nsats)) {
+        field_not_found(msg, "NSats");
+    }
     gps.setHIL(gps_offset,
                (AP_GPS::GPS_Status)status,
                uint32_t(time_us/1000),
                loc,
                vel,
-               require_field_uint8_t(msg, "NSats"),
+               nsats,
                hdop,
                require_field_float(msg, "VZ") != 0);
     if (status == AP_GPS::GPS_OK_FIX_3D && ground_alt_cm == 0) {

Tools/Replay/MsgHandler.h

@@ -67,7 +67,6 @@ private:
     void init_field_types();
     void add_field_type(char type, size_t size);
     uint8_t size_for_type(char type);
-    void field_not_found(uint8_t *msg, const char *label);
 
 protected:
     struct log_Format f; // the format we are a parser for
@@ -87,6 +86,7 @@ protected:
 			   const char *label_roll,
 			   const char *label_pitch,
 			   const char *label_yaw);
+    void field_not_found(uint8_t *msg, const char *label);
 };
 
 template<typename R>