Use result even when results is empty in sim

[abdulrabbani00]

Right now if you run a sim you can get the following result:

$ curl https://35.221.121.54.sslip.io/simulate/solana/mainnet-beta/4Hmd6PdjVA9auCoScE12iaBogfwS4ZXQ6VZoBeqanwWW
[{"feed":"4Hmd6PdjVA9auCoScE12iaBogfwS4ZXQ6VZoBeqanwWW","feedHash":"1f42dfb21efb24828b99fbe70e6d139cd665aafcbb1706bccd8f2a9b12562db6","results":[],"result":"118.22250000","stdev":"0","variance":"0"}]   

With the current implementation, this entire result is thrown away because the library does not parse the decimal in result and because results is empty.

This is an opinionated approach:

1. If result exists, use that.
2. If result does not exist, get the median from results.

You could also do the inverse:

1. If results exist, get the median and overwrite result.
2. If results does not exist, use the existing result.

There is also a third option which is to do nothing when result is none and let the downstream user handle it all.

I prefer the proposed approach as it allows the caller to get both raw values and decide what they want to do.