All the ones I've ever signed had an exception list for previous IP. You can sign it as is, just make sure your exceptions include all your previous work. You try something like, "Excluding any work or IP made or started before employment with xyz." "Excluding any work not explicitly requested by company xyz, etc." That way you can sign it as is but use the exceptions section.

You have to ask yourself, is working for that company worth giving them explicit rights for all your prior work you've done for yourself? That's exactly what they are asking for in most cases. Let's say you make it big with something you wrote before you even started working there and they find out. They can take it right from under you if you sign that contract without exceptions. Just know what you are getting into and what they are really asking you to commit to.

I actually left a job because I wanted to start a new project and I had signed a similar document without an exception. I didn't want them to have any claim with the IP. Also know, any investors will probably shy away from you if you've signed away your IP rights like that.