Update Marlin_main.cpp - Workaround for Change Filament Carriage Movemen...

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This is a workaround solution for issue #1038 (Change Filament Disables X and Y Steppers Which Cuases Carriage Movement While Changing Filament)

Starting from line 3606 enable commands are added for x,y,z axis steppers just after the call of manage_inactivity procedure. Manage_inactivity procedure disables the steppers and just after it steppers are enabled again.