Fix possible function typo in function_at

[nazywam]

It seems that there might be an unintended typo in function_at

Because the iteration is done on a new generator (Functions()) instead of the initialized one (functions) it will always return the address of the first function:

Python>function_at(0x00000001800257D1)
0x180001060
Python>function_at(0x000000018002C950)
0x180001060
Python>function_at(0x000000018002A8D0)
0x180001060

I tried to fix it by making minimal changes but it can also be written nicely as

def function_at(ea):
    return next(Functions(ea), None)

[hasherezade]

Thanks!