display.cpp: do not show SAT if no NMEA data seen

src/display.cpp

@@ -156,6 +156,8 @@ void refreshtheDisplay() {
 
 // update GPS status (line 2)
 #ifdef HAS_GPS
+    // have we ever got valid gps data?
+    if (gps.passedChecksum() > 0) {
       u8x8.setCursor(9, 2);
       if (!gps.location.isValid()) // if no fix then display Sats value inverse
       {
@@ -164,6 +166,7 @@ void refreshtheDisplay() {
         u8x8.setInverseFont(0);
       } else
         u8x8.printf("Sats:%.2d", gps.satellites.value());
+    }
 #endif
 
     // update bluetooth counter + LoRa SF (line 3)