add in empty modifier slot so dynamic paint files don't break.

source/blender/makesdna/DNA_modifier_types.h

@@ -74,6 +74,7 @@ typedef enum ModifierType {
 	eModifierType_WeightVGEdit,
 	eModifierType_WeightVGMix,
 	eModifierType_WeightVGProximity,
+	eModifierType_EmptySlot,    /* keep so DynamicPaint keep loading, can re-use later */
 	eModifierType_DynamicPaint, /* reserve slot */
 	NUM_MODIFIER_TYPES
 } ModifierType;