Prevent altitude override without coordinates

Altitude should not be overriden with default value as it is defined without
knowing the field or the flight conditions. Therefore the user has to provide
coordinates with the desired altitude so altitude override can happen.

mavsdk_wrapper.cpp

@@ -193,6 +193,11 @@ static int doOverride(float altitude, float speed, const char* failure_msg) {
     if (!mavsdk_started)
         return -1;
 
+    if (!first_coordinate_entered) {
+        log_error("Not overriding altitude before user sets coordinates");
+        return -1;
+    }
+
     MavlinkPassthrough::CommandLong command;
     command.command = MAV_CMD_DO_OVERRIDE;
     command.param1 = 1 | 2 | 4 | 8;