Active Control max velocity default value fix

[olivecha]

The default value for m_ctrl_velMax was set to -1.0 in PeleLM.H

The updated velocity in PeleLMFlowControler.cpp is not limited by the maximum velocity parameter if the parameter value is less than zero.

This result in the active_control.velMax input file parameter being truly optional (see issue #232).

Active control was able to converge without setting the active_control.velMax parameter:

[baperry2]

Thanks for doing this!

Can you also modify the docs here to reflect the slightly updated behavior?
https://github.com/AMReX-Combustion/PeleLMeX/blob/62b496ca0abf7bad0ef971cb53fde6eb0226a781/Docs/source/manual/LMeXControls.rst?plain=1#L387C11-L387C11

Closes #232

[baperry2]

Thanks again, this should be good assuming all the tests pass.