We bail out later on since we didn't find the required CRL, but before
that there is a calloc(1, 0) which we should avoid, so this makes the
code more robust. Inspired by FORT's latest DoS pointed out by job.

Index: mft.c
===================================================================
RCS file: /cvs/src/usr.sbin/rpki-client/mft.c,v
diff -u -p -r1.120 mft.c
--- mft.c	2 Nov 2024 12:30:28 -0000	1.120
+++ mft.c	22 Dec 2024 14:52:23 -0000
@@ -373,6 +373,10 @@ mft_parse_econtent(const char *fn, struc
 		goto out;
 	}
 
+	if (sk_FileAndHash_num(mft_asn1->fileList) <= 0) {
+		warnx("%s: no files in manifest fileList", fn);
+		goto out;
+	}
 	if (sk_FileAndHash_num(mft_asn1->fileList) >= MAX_MANIFEST_ENTRIES) {
 		warnx("%s: %d exceeds manifest entry limit (%d)", fn,
 		    sk_FileAndHash_num(mft_asn1->fileList),