Crash when move after 2 G28 X0 in Duplication mode

[murdock62]

Originally reported by Buriaku

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
G28 ; home all
M605 S2 ; activate copy mode
G1 Z10 ; don't collide with bed
G28 X0 ; home x to activate copy mode
G1 X10 ; move both heads

It works like it should. But if you then do:
G28 X0
G1 X10

E1 will crash to the endstop.

Expected behavior
The two extruders must move simultaneously.

[murdock62]

Seem to be fixed by modifying the g28.cpp file like this:

Before :
extruder_duplication_enabled = IDEX_saved_duplication_state;

After :
//extruder_duplication_enabled = IDEX_saved_duplication_state;

I think this will fix the issue # 33 too.

[klack]

Need to reverify