how to iteratively loft wires in cadquery 2?

Same post as [here](https://github.com/dcowden/cadquery/issues/307). I can loft a 2D shape from one plane to another like this:

```
import cadquery as cq
from jupyter_cadquery.cadquery import show
result = cq.Workplane("XY").rect(1,2).workplane() \
.transformed(offset=cq.Vector(0, -0.5, 1.0),rotate=cq.Vector(10, 0, 0)) \
.rect(1,2).loft(combine=True)
show(result)

```
image

I would like to repeat the operation several times like this:

```
import cadquery as cq
from jupyter_cadquery.cadquery import show

wp = cq.Workplane("XY").rect(1,2).workplane()
result = None
for i in range(0,5):
wp2 = wp.transformed(offset=cq.Vector(0, -0.5, 1.0),rotate=cq.Vector(10, 0, 0))
if result == None:
result = wp2.rect(1,2).loft(combine=True)
else:
nextpart = wp2.rect(1,2).loft(combine=True)
result = result.union(nextpart)
wp = wp2
show(result)
```

I have the following error:

```
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
in
9 result = wp2.rect(1,2).loft(combine=True)
10 else:
---> 11 nextpart = wp2.rect(1,2).loft(combine=True)
12 result = result.union(nextpart)
13 wp = wp2

~/anaconda3/envs/cq-jl/lib/python3.7/site-packages/cadquery/cq.py in loft(self, filled, ruled, combine)
2897 self.ctx.pendingWires = []
2898
-> 2899 r = Solid.makeLoft(wiresToLoft, ruled)
2900
2901 if combine:

~/anaconda3/envs/cq-jl/lib/python3.7/site-packages/cadquery/occ_impl/shapes.py in makeLoft(cls, listOfWire, ruled)
1594 # the True flag requests building a solid instead of a shell.
1595 if len(listOfWire) < 2:
-> 1596 raise ValueError("More than one wire is required")
1597 loft_builder = BRepOffsetAPI_ThruSections(True, ruled)
1598

ValueError: More than one wire is required
```

At least, If I suppress the for loop and keep the same variable decomposition, it works:

```
import cadquery as cq
from jupyter_cadquery.cadquery import show

wp = cq.Workplane("XY").rect(1,2).workplane()
wp2 = wp.transformed(offset=cq.Vector(0, -0.5, 1.0),rotate=cq.Vector(10, 0, 0))
result = wp2.rect(1,2).loft(combine=True)
wp = wp2
show(result)
```

I think I am close to the result, but I cannot find where I mistake myself. The problem occurs when I come in the loop the second time. I think I have accumulated already two wires in wp2. I should keep only the last one before adding a new one, but I don't know how to do it.