Fix nil pointer dereference when sensor is not connected/initialized and webUI sensor option is disabled.

2017/03/28 13:43:00 wrote settings.
2017/03/28 13:43:01 http: panic serving 192.168.10.12:52012: runtime
error: invalid memory address or nil pointer dereference
goroutine 83 [running]:
net/http.(*conn).serve.func1(0x10ab6ae0, 0x73826140, 0x10d8c708)
	/root/go-1.5.1/src/net/http/server.go:1287 +0x9c
main.handleSettingsSetRequest(0x72ec00b0, 0x10d93580, 0x10db0620)
	/root/stratux-westphae/main/managementinterface.go:286 +0x1620
net/http.HandlerFunc.ServeHTTP(0x5d2ecc, 0x72ec00b0, 0x10d93580,
0x10db0620)
	/root/go-1.5.1/src/net/http/server.go:1422 +0x34
net/http.(*ServeMux).ServeHTTP(0x10960dc0, 0x72ec00b0, 0x10d93580,
0x10db0620)
	/root/go-1.5.1/src/net/http/server.go:1699 +0x164
net/http.serverHandler.ServeHTTP(0x109c4300, 0x72ec00b0, 0x10d93580,
0x10db0620)
	/root/go-1.5.1/src/net/http/server.go:1862 +0x190
net/http.(*conn).serve(0x10ab6ae0)
	/root/go-1.5.1/src/net/http/server.go:1361 +0xbfc
created by net/http.(*Server).Serve
	/root/go-1.5.1/src/net/http/server.go:1910 +0x360
2017/03/28 13:43:01 http: panic serving 192.168.10.12:52013: runtime
error: invalid memory address or nil pointer dereference
goroutine 58 [running]:
net/http.(*conn).serve.func1(0x1098b4a0, 0x73826140, 0x10de8228)
	/root/go-1.5.1/src/net/http/server.go:1287 +0x9c
main.handleSettingsSetRequest(0x72ec00b0, 0x10d93680, 0x10db0690)
	/root/stratux-westphae/main/managementinterface.go:286 +0x1620
net/http.HandlerFunc.ServeHTTP(0x5d2ecc, 0x72ec00b0, 0x10d93680,
0x10db0690)
	/root/go-1.5.1/src/net/http/server.go:1422 +0x34
net/http.(*ServeMux).ServeHTTP(0x10960dc0, 0x72ec00b0, 0x10d93680,
0x10db0690)
	/root/go-1.5.1/src/net/http/server.go:1699 +0x164
net/http.serverHandler.ServeHTTP(0x109c4300, 0x72ec00b0, 0x10d93680,
0x10db0690)
	/root/go-1.5.1/src/net/http/server.go:1862 +0x190
net/http.(*conn).serve(0x1098b4a0)
	/root/go-1.5.1/src/net/http/server.go:1361 +0xbfc
created by net/http.(*Server).Serve
	/root/go-1.5.1/src/net/http/server.go:1910 +0x360

main/managementinterface.go

@@ -276,13 +276,13 @@ func handleSettingsSetRequest(w http.ResponseWriter, r *http.Request) {
 						globalSettings.GPS_Enabled = val.(bool)
 					case "IMU_Sensor_Enabled":
 						globalSettings.IMU_Sensor_Enabled = val.(bool)
-						if !globalSettings.IMU_Sensor_Enabled {
+						if !globalSettings.IMU_Sensor_Enabled && globalStatus.IMUConnected {
 							myIMUReader.Close()
 							globalStatus.IMUConnected = false
 						}
 					case "BMP_Sensor_Enabled":
 						globalSettings.BMP_Sensor_Enabled = val.(bool)
-						if !globalSettings.BMP_Sensor_Enabled {
+						if !globalSettings.BMP_Sensor_Enabled && globalStatus.BMPConnected {
 							myPressureReader.Close()
 							globalStatus.BMPConnected = false
 						}
@@ -397,8 +397,8 @@ func handleOrientAHRS(w http.ResponseWriter, r *http.Request) {
 	if r.Method == "POST" {
 		var (
 			action []byte = make([]byte, 1)
-			u int
-			err error
+			u      int
+			err    error
 		)
 
 		if _, err = r.Body.Read(action); err != nil {
@@ -422,7 +422,7 @@ func handleOrientAHRS(w http.ResponseWriter, r *http.Request) {
 			}
 			log.Printf("AHRS Info: sensor orientation: received up direction %d\n", u)
 
-			if f==u || f==-u {
+			if f == u || f == -u {
 				log.Println("AHRS Error: sensor orientation: up and forward axes cannot be the same")
 				http.Error(w, "up and forward axes cannot be the same", http.StatusBadRequest)
 				return