Emit pass for empty blocks in generated Python

[mattibat]

Any empty block (a one-sided falls, an empty loop body, an empty fall, ...) produced Python that fails with an IndentationError:

if a > b:
    print(a)
else:

Empty bodies now get pass, and an empty else is left out entirely:

if a > b:
    print(a)

Java and JavaScript output is unchanged.

[mikebarkmin]

thx