Generate a zero-length signature for symlinks

The fsverity utility follows the symlink when generating a signature.
Since we don't want to sign the same file twice, we need to skip these
links, and instead just generate a dummy zero-length signature here.

Signed-off-by: Jes Sorensen <jsorensen@fb.com>

sign/rpmsignverity.c

@@ -45,7 +45,10 @@ static char *rpmVeritySignFile(rpmfi fi, size_t *sig_size, char *key,
     uint8_t *sig = NULL;
     int status;
 
-    file_size = rpmfiFSize(fi);
+    if (S_ISLNK(rpmfiFMode(fi)))
+	file_size = 0;
+    else
+	file_size = rpmfiFSize(fi);
 
     memset(&params, 0, sizeof(struct libfsverity_merkle_tree_params));
     params.version = 1;