Bugfix #2122

This version restore a behavior of v4.9.4 where, if it is not possible to read the configuration from the machine (rare and wrong case, but existing) a value of 1000 is assumed for $30 Max PWM. This fix some issue that few user is having using v5.x

Note to the reader: it's not really a LaserGRBL bug! If configuration can't be read is a problem of the machine firmware.
I only put a patch on it!