gh-118609: Add proper error check for framelocalsproxy

[gaogaotiantian]

• Completed error checks in frameobject.c
• Fixed the compiler warning for unused variables
• Polished the declarations a bit so the error checks are closer to the declared variable, and variables are declared in the necessary scope

• Issue: Objects/frameobject.c lacks error-checking #118609

[gvanrossum]

Thanks! One style nit, you can fix it or leave it.

(Maybe @sobolevn can review too, in case I missed anything -- I realize I am not up to speed with all the details of writing this kind of code any more.)

[gvanrossum]

I'd swap these two lines, so that the Py_ReprEnter/Leave and the PyDict_New/Py_DECREF "brackets" properly nest. But this works too of course.

[gaogaotiantian]

Yeah that makes sense. DECREF dct as soon as we are done with it and then leave repr. Fixed it.

[gvanrossum]

(Maybe @sobolevn can review too, in case I missed anything -- I realize I am not up to speed with all the details of writing this kind of code any more.)

I meant @Eclips4 of course, since he reported the issue. (But Nikita is also welcome! :-)

[gvanrossum]

I'll merge everything Monday morning (Pacific time) unless anyone says otherwise.

[Eclips4]

LGTM!

[sobolevn]

Thank you!