signed vs. unsigned in plpy_procedure.c

Hi,

src/postgresql/src/pl/plpython/plpy_procedure.c: In function ‘PLy_procedure_munge_source’:
src/postgresql/src/pl/plpython/plpy_procedure.c:507:2: warning: comparison of unsigned expression >= 0 is always true
[-Wtype-limits]
  Assert(plen >= 0 && plen < mlen);

Which has a point, we assign sprintf()s result to a size_t and then
check for a negative value. Which doesn't work.

Obviously the impact is miniscule, but removing legitimate warnings is a
good thing. Trivial patch attached.

Greetings,

Andres Freund

--
 Andres Freund                       http://www.2ndQuadrant.com/
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