node-http: add check for height being below tip

This commit simply adds an enforce line to check that the height being
requested to reset to is below the chain tip. This way we return a bad
request error rather than a internal server error.

lib/node/http.js

@@ -339,6 +339,8 @@ class HTTP extends Server {
       const height = valid.u32('height');
 
       enforce(height != null, 'Height is required.');
+      enforce(height <= this.chain.height,
+        'Height cannot be greater than chain tip.');
 
       await this.chain.reset(height);