fix inventory edit weight bug - fix inventory document - set new validations for distribution

apps/warehouse/web/api/v1/serializers.py

@@ -42,8 +42,12 @@ class InventoryEntrySerializer(serializers.ModelSerializer):
             total=models.Sum('weight')
         )['total'] or 0
 
-        if total_entered + attrs['weight'] > distribution.weight:
-            raise InventoryEntryWeightException()
+        if self.instance.weight is 0:
+            if total_entered + attrs['weight'] > distribution.weight:
+                raise InventoryEntryWeightException()
+        elif self.instance.weight is not 0:
+            if total_entered - self.instance.weight + attrs['weight'] > distribution.weight:
+                raise InventoryEntryWeightException()
 
         return attrs