no detection of undefined parameters in else branches

pyflakes correctly warns on using x before defining it in the if branch:

def bar(a):
    pass

def x_is_bad_if():
    if False:
        x = bar(x)
    else:
        x = bar(1)

    return x

However, no warning is generated for the else branch:

def bar(a):
    pass

def x_is_bad_else():
    if False:
        x = bar(1)
    else:
        x = bar(x)

    return x