Follow up on @angular-devkit/build-angular spec_large error

[filipesilva]

This should really be using Ivy but was getting the error below on every second build.
ERROR in Cannot read property 'incrementalState' of null

See 0a4dd9b

[filipesilva]

@clydin looked into this and it seems to be related to the Ivy compiler checking for undefined explicitely:
https://github.com/angular/angular/blob/cd7b1992193be85f3317a4ef793b13c03ac2b215/packages/compiler-cli/src/ngtsc/program.ts#L161

But it seems that in @ngtools/webpack we set it to null in some cases. Those should change.

We should figure out why it happens on every second test only though.

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