pem: Fix assert condition

If the PEM header is "-----BEGIN -----", *type should be an empty
string and the parser shouldn't fail.  Reported by Han Han in:
https://bugzilla.redhat.com/show_bug.cgi?id=1665172

trust/pem.c

@@ -84,7 +84,7 @@ pem_find_begin (const char *data,
 
 	if (type) {
 		pref += ARMOR_PREF_BEGIN_L;
-		assert (suff > pref);
+		assert (suff >= pref);
 		*type = strndup (pref, suff - pref);
 		return_val_if_fail (*type != NULL, NULL);
 	}

trust/test-pem.c

@@ -119,6 +119,24 @@ struct {
 	  }
 	},
 
+	{
+	  /* one block with empty type */
+	  "-----BEGIN -----\n"
+	  "aYNNXqshlVxCdo8QfKeXh3GUzd/yn4LYIVgQrx4a\n"
+	  "-----END -----",
+	  {
+	    {
+	      "",
+	      "\x69\x83\x4d\x5e\xab\x21\x95\x5c\x42\x76\x8f\x10\x7c\xa7\x97\x87"
+	      "\x71\x94\xcd\xdf\xf2\x9f\x82\xd8\x21\x58\x10\xaf\x1e\x1a",
+	      30,
+	    },
+	    {
+	      NULL,
+	    }
+	  }
+	},
+
 	{
 	  NULL,
 	}