Fix pg_strtof() to not crash on NULL endptr.
We had managed not to notice this simple oversight because none
of our calls exercised the case --- until commit
8f427187d.
That led to pg_dump crashing on any platform that uses this code
(currently Cygwin and Mingw).
Even though there's no immediate bug in the back branches, backpatch,
because a non-POSIX-compliant strtof() substitute is trouble waiting
to happen for extensions or future back-patches.
Diagnosed-by: Alexander Lakhin <exclusion@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/
339b3902-4e98-4e31-a744-
94e43b7b9292@gmail.com
Backpatch-through: 13