Don't forget to init mavsdkServerHandle

Author: JonasVautherin

mavsdk_server/src/main/java/io/mavsdk/mavsdkserver/MavsdkServer.java

@@ -54,6 +54,7 @@ public int run(String systemAddress) {
    *     A return value of 0 means that the server failed to start.
    */
   public int run(String systemAddress, int mavsdkServerPort) {
+    mavsdkServerHandle = initNative();
 
     if (!runNative(mavsdkServerHandle, systemAddress, mavsdkServerPort)) {
       return 0;