[PATCH] Fix potential memoryleak in guc.c

Hi all

In src\backend\utils\misc\guc.c, I found a potential memory leak.

make_absolute_path() return a malloc'd copy, we should free memory before the function return false.
----------------------------------------------------------------------------
SelectConfigFiles(const char *userDoption, const char *progname)
{
......
/* configdir is -D option, or $PGDATA if no -D */
if (userDoption)
configdir = make_absolute_path(userDoption); ★
else
configdir = make_absolute_path(getenv("PGDATA")); ★

if (configdir && stat(configdir, &stat_buf) != 0)
{
write_stderr("%s: could not access directory \"%s\": %s\n",
progname,
configdir,
strerror(errno));
if (errno == ENOENT)
write_stderr("Run initdb or pg_basebackup to initialize a PostgreSQL data directory.\n");
★// Need to free memory of configdir
return false;
}
......
---------------------------------------------------------------------------

Refer to the following files for the implementation of make_absolute_path().

file: src\port\path.c
/*
* make_absolute_path
*
* If the given pathname isn't already absolute, make it so, interpreting
* it relative to the current working directory.
*
* Also canonicalizes the path. The result is always a malloc'd copy.