py/compile: Fix potential Py-stack overflow in try-finally with return.

If a return is executed within the try block of a try-finally then the
return value is stored on the top of the Python stack during the execution
of the finally block.  In this case the Python stack is one larger than it
normally would be in the finally block.

Prior to this commit, the compiler was not taking this case into account
and could have a Python stack overflow if the Python stack used by the
finally block was more than that used elsewhere in the function.  In such
a scenario the last argument of the function would be clobbered by the
top-most temporary value used in the deepest Python expression/statement.

This commit fixes that case by making sure enough Python stack is allocated
to the function.

Fixes issue #13562.

Signed-off-by: Damien George <damien@micropython.org>

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