Merge pull request #1798 from thinkyhead/fixup_probing

Fix probe height at G28 start

Marlin/Marlin_main.cpp

 
           // raise extruder
           float measured_z,
-                z_before = Z_RAISE_BETWEEN_PROBINGS + (probePointCounter ? current_position[Z_AXIS] : 0);
+                z_before = probePointCounter ? Z_RAISE_BETWEEN_PROBINGS + current_position[Z_AXIS] : Z_RAISE_BEFORE_PROBING;
 
           #ifdef DELTA
             // Avoid probing the corners (outside the round or hexagon print surface) on a delta printer.