fix: zero attr

[nobkd]

closes #248 with b94f03b

You can see this example errors, if not for the change in render.js. Just undo that change and run bun test to see sth like this:

See error log

41 |             ret += `${str.substring(lastIdx, i)}&#x${getCodePoint(str, i).toString(16)};`;
42 |             // Increase by 1 if we have a surrogate pair
43 |             lastIdx = xmlReplacer.lastIndex += Number((char & 0xfc00) === 0xd800);
44 |         }
45 |     }
46 |     return ret + str.substr(lastIdx);
                      ^
TypeError: str.substr is not a function. (In 'str.substr(lastIdx)', 'str.substr' is undefined)
      at encodeXML (/home/nobkd/<pth>/nue/node_modules/entities/lib/esm/escape.js:46:18)
      at /home/nobkd/<pth>/nue/node_modules/dom-serializer/lib/esm/index.js:49:27
      at map (:1:21)
      at formatAttributes (/home/nobkd/<pth>/nue/node_modules/dom-serializer/lib/esm/index.js:38:12)
      at renderTag (/home/nobkd/<pth>/nue/node_modules/dom-serializer/lib/esm/index.js:142:21)
      at render (/home/nobkd/<pth>/nue/node_modules/dom-serializer/lib/esm/index.js:89:19)
      at render (/home/nobkd/<pth>/nue/node_modules/dom-serializer/lib/esm/index.js:89:19)
      at render (/home/nobkd/<pth>/nue/packages/nuejs/src/render.js:364:23)
      at runTests (/home/nobkd/<pth>/nue/packages/nuejs/test/render.test.js:8:18)
      at /home/nobkd/<pth>/nue/packages/nuejs/test/render.test.js:146:3

---

test falsy values with b918eb2 (test for something like #193 fixed by a3b29f5)

[tipiirai]

Thanks!