cont_regr with both filter and mult break

[gdementen]

- value: cont_regr(2.4 + 0.22 * age, mult=0.5, filter=age > 10)

results in:
ERROR: DFC // dynamicfunctioncall(normal(0, 1).dtype, None)
(or with earlier versions):
ERROR: normal(loc=0, scale=1).dtype(<context.EntityContext object at 0x066D07D0>)

[gdementen]

For a test case, see: https://gist.github.com/gdementen/e629dce747efab334b69

In 0.9, the following workaround works:

- value: cont_regr(2.4 + 0.22 * age + 0.5 * normal(), filter=age > 10)

However, this workaround apparently does not work in 0.8.1.