Fix count_direction initializer

- Addressing #1625

Marlin/stepper.cpp

 static bool check_endstops = true;
 
 volatile long count_position[NUM_AXIS] = { 0 };
-volatile signed char count_direction[NUM_AXIS] = { 1 };
+volatile signed char count_direction[NUM_AXIS] = { 1, 1, 1, 1 };
 
 
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