LGTM.com - false positive: unable to infer presence of `__call__` overload

**Description of the false positive**
The lines in question are:
```python
L21 = layout.MultiVector(...)
L12 = layout.MultiVector(...)
K = L21 + L12 + 2.0
beta = K(4) # Call to a non-callable of builtin-class float.
```
Where:
* `layout.MultiVector` returns an instance of `MultiVector`
* `MultiVector.__add__` is overloaded to return an instance of `MultiVector`
* `MultiVector.__call__` is defined

**URL to the alert on the project page on LGTM.com**

https://lgtm.com/projects/g/pygae/clifford/snapshot/23c8649145cc81a9a44e7b0e445d7e000639101e/files/clifford/tools/g3c/__init__.py#x3c80edcfa911a30d:1