Possible infinite recursion

[deiuch]

https://github.com/Denchick777/expression-parser/blob/da36070dd5f5e896a923345194055901ac4adba4/PrimaryExp.java#L41-L47

Possible case: ()

[deiuch]

Probably, it is not an issue because of this check:
https://github.com/Denchick777/expression-parser/blob/da36070dd5f5e896a923345194055901ac4adba4/PrimaryExp.java#L51-L53