Bug report

After updating PHPStan from 1.3.1 to 1.4.1 assigning to a readonly property in the different branches of the same condition (if-else) is started to false trigger the error "Readonly property is already assigned".

Code snippet that reproduces the problem

https://phpstan.org/r/2069a468-0e58-4991-a125-69f1ce64f7a3

Expected output

No error should be reported.