Bug in interp_Lwhile.py: missing return in interpreter definition.

[elavoie]

Missing 'return' for the body case.

Without this 'return' the following code prints 'None' instead of '9':

def func(a: int) -> int:
    i = True

    while i:
       a = a - 1
       i = False

    # print(a) at this point will print 9
    return a

print(func(10)) # expected 9, got None