[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:

if (0) write(*, *) 'Test is false'
if (1) write(*, *) 'Test is true'

A slightly more meaningful example

integer val
val = 1
if (val) write(*, *) 'Test is true'

This should be replaced by

integer val
val = 1
if (val > 0) write(*, *) 'Test is true'