Fix thinko when bumping on temporary directories in pg_checksums

This fixes an oversight from 5c99513.  This has no actual consequence as
PG_TEMP_FILE_PREFIX and PG_TEMP_FILES_DIR have the same value so when
bumping on a temporary path the directory scan was still moving on to
the next entry instead of skipping the rest of the scan, but let's keep
the logic correct.

Author: Michael Banck
Reviewed-by: Kyotaro Horiguchi
Discussion: https://postgr.es/m/20190314.115417.58230569.horiguchi.kyotaro@lab.ntt.co.jp
Backpatch-through: 11

Author: michaelpq

src/bin/pg_checksums/pg_checksums.c

@@ -171,7 +171,7 @@ scan_directory(const char *basedir, const char *subdir)
 		if (strncmp(de->d_name,
 					PG_TEMP_FILES_DIR,
 					strlen(PG_TEMP_FILES_DIR)) == 0)
-			return;
+			continue;
 
 		snprintf(fn, sizeof(fn), "%s/%s", path, de->d_name);
 		if (lstat(fn, &st) < 0)