[Fortran] Replace `if (integer)` with `if (logical)`

In Fortran there is no equivalence between logical and integer variables, so `0` is not a replacement for `.false.`, and `1` does not replace `.true.`. Yet, some compilers (ifort) will happily compile `if (1)`.

Example:
```fortran
if (0) write(*, *) 'Test is false'
if (1) write(*, *) 'Test is true'
```

A slightly more meaningful example
```fortran
integer val
val = 1
if (val) write(*, *) 'Test is true'
```
This should be replaced by
```fortran
integer val
val = 1
if (val > 0) write(*, *) 'Test is true'
```