pacman-key: return 0 from get_from if default value used

This prevents the error trap being set off when GPGDir is commented
in pacman.conf.  Bug introduced in 507b01b9.

Signed-off-by: Allan McRae <allan@archlinux.org>
Signed-off-by: Dan McGee <dan@archlinux.org>

scripts/pacman-key.sh.in

@@ -106,7 +106,10 @@ get_from() {
 			return 0
 		fi
 	done < "$1"
-	printf '%s\n' "$3"
+	if [[ -n "$3" ]]; then
+		printf '%s\n' "$3"
+		return 0
+	fi
 	return 1
 }