Really? Dropbox is the only company that I know of and when Dropbox started in Ycombinator they were already a two-man team? I'm really interested in knowing the other companies that were only funded as a single founder company
https://duckduckgo.com/?q=single+founder+y+combinator+compan...
Again, it's definitely a strike against you in the selection process (as it probably should be...I've started a company solo and I've started a company with a co-founder...the latter is clearly better), but it's not a deal-breaker.