Account fetch: add error handling about solana-playground

[acheroncrypto]

Awesome! Few things to add:

1. Would be nice to have public key validation like in the instructions section. If you put an invalid public key, the input should error.
   

2. Button should be disabled on error public key error or if the playground wallet is not connected like in the instructions section.

3. If the error occured during an rpc request, I think it's best to show the error message in the result section.