Updated FreeBSD package name in readme [skip ci]

README.md

@@ -1233,7 +1233,7 @@ Note: Replace `18` with your Postgres server version
 Install the FreeBSD package with:
 
 ```sh
-pkg install postgresql17-pgvector
+pkg install postgresql18-pgvector
 ```
 
 or the port with:

src/ivfutils.c

@@ -25,8 +25,8 @@ VectorArrayInit(int maxlen, int dimensions, Size itemsize)
 {
 	VectorArray res;
 
-	if (maxlen < 1 || dimensions < 1)
-		elog(ERROR, "safety check failed");
+	if (maxlen < 1 || dimensions < 1 || itemsize == 0)
+		elog(ERROR, "cannot create vector array");
 
 	/* Ensure items are aligned to prevent UB */
 	itemsize = MAXALIGN(itemsize);