Be less strict about the length of the version string

This caused a test failure when using a tarball produced
by the "make source_package" command. I believe the
version string was "2.6.1" which is less than the 8 characters
the test expected.

Author: mheily

test/libkqueue.c

@@ -46,8 +46,8 @@ test_libkqueue_version_str(struct test_context *ctx)
         die("kevent");
     }
 
-    if (strlen((char *)receipt.udata) < 8) {
-        printf("No version number returned");
+    if (!strlen((char *)receipt.udata)) {
+        printf("empty version number returned");
         die("kevent");
     }
 }