Python minor cleanups

Noticed redundant #ifndef's during investigation of #1756.  Since almost
all code within fontforge/python.c is surrounded by `#ifndef _NO_PYTHON`
it was strange to see individual bits of code surrounded by additional
such `#ifndefs`

Also, one copy-n-paste was one line too low, with an `exit(0)` before it.

And just happened to notice an extra unneeded declaration in
fontforgeexe/startui.c  Do modern C compilers just drop those?  And wow,
Coverity didn't complain either.
Python Py_BuildValue() bad zero values

Reading through old changes to fontforge/python.c I saw change 94b6ccb9484eb85fe25c5e127ce33175e1118a67
which intrigued me, telling me something I didn't know about using the
Python C API Py_BuildValue().  His descriptions included
> Integers being incorrectly passed to Py_BuildValue() expecting double.
>   The fix is to substitute 0.0 for 0 in these arguments, which C treats
>   as constant of type double.

But when you find one instance of a bad pattern, you should worry
whether that same goof was reproduced in multiple.  (Un?)fortunately
this same mistake was found in 3 more places.  These were changed
like this:
>     return( Py_BuildValue("(dddd)", 0,0,0,0 ));

to
>     return( Py_BuildValue("(dddd)", 0.0, 0.0, 0.0, 0.0 ));

One instance was easily tested, and indeed found to be broken and then
fixed by this change:
>  contour.boundingBox() returned '(6.91320453175617e-310, 6.91320569035315e-310, 6.9132056837544e-310, 1e-323)'

vs.
>  contour.boundingBox() returned '(0.0, 0.0, 0.0, 0.0)'
Merge pull request #1766 from tshinnic/python_cleanup_misc_1

Python cleanup misc 1