'Turbo' does not use default scale values when `axis_linear` and `axis_angular` are set

[Dave Kroezen]

The documentation seems to imply that when the enable_turbo_button parameter is set correctly, the default value for scale_linear_turbo is set equal to 1.0 (scale_angular_turbo is not even mentioned). I currently encounter a case where this is not the case.

Using the following configuration teleop_ps4, the enable_turbo_button is causing the teleop_twist_joy_node to start publishing Twist messages as expected, but with all fields being zero even while receiving the correct values on the joy topic used as input.

Looking at teleop_twist_joy.cpp:77 this seems to be because the code does not use default values when axis_linear (or axis_angular) are set.

Is this intentional and does the documentation just need an update? Otherwise, I can suggest a fix for this issue and submit a PR.