Fix for the PR #5255 (Case light menu (3rd attempt))

[ghost]

Fix for the PR #5255 (Case light menu (3rd attempt))

When try to use a case light without LCD, compilation error occurs.

error message

\AppData\Local\Temp\arduino_build_104836\sketch\Marlin_main.cpp: In function 'void update_case_light()':

Marlin_main.cpp:7501: error: 'case_light_on' was not declared in this scope

     digitalWrite(CASE_LIGHT_PIN, case_light_on != INVERT_CASE_LIGHT ? HIGH : LOW);

                                  ^

\AppData\Local\Temp\arduino_build_104836\sketch\Marlin_main.cpp: In function 'void gcode_M355()':

Marlin_main.cpp:7513: error: 'case_light_on' was not declared in this scope

     if (code_seen('S')) case_light_on = code_value_bool();

                         ^

Marlin_main.cpp:7517: error: 'case_light_on' was not declared in this scope

     case_light_on ? SERIAL_ECHOLNPGM("on") : SERIAL_ECHOLNPGM("off");

     ^