Fix issue with memory allocations in lisp::serialise

Was to do with sv_make.

lisp/lisp.c

@@ -252,7 +252,13 @@ sv_t serialise(context_t *ctx, lisp_t *ptr)
         lmember = CAR(lmember);
 
       sv_t member = serialise(ctx, lmember);
-      s           = sv_concat(&ctx->scratch, s, member);
+      if (!s.data)
+        s = member;
+      else
+        s = sv_concat(&ctx->scratch, s, member);
+
+      // NOTE: eventually this separator we add per item should be mutable at
+      // runtime.
       if (IS_TAG(lsp, CONS) && !CDR(lsp))
         continue;
       else if (IS_TAG(CDR(lsp), CONS))