Merge pull request #6490 from Bob-the-Kuhn/Missing-X-stop

Endstop not enabled if pin is zero

Marlin/Conditionals_post.h

     #endif
   #endif
 
-  #define IS_Z2_OR_PROBE(P) (P == Z2_MIN_PIN || P == Z2_MAX_PIN || P == Z_MIN_PROBE_PIN)
+  #define IS_Z2_OR_PROBE(P) (PIN_EXISTS(Z2_MIN_PIN)      && (P == Z2_MIN_PIN) \
+                          || PIN_EXISTS(Z2_MAX_PIN)      && (P == Z2_MAX_PIN) \ 
+                          || PIN_EXISTS(Z_MIN_PROBE_PIN) && (P == Z_MIN_PROBE_PIN))
 
   /**
    * Set ENDSTOPPULLUPS for active endstop switches