store-histogram: skip not found file meta

[HaoranYi]

Problem

store-histogram crash on not found file meta.

thread 'main' panicked at accounts-db/store-histogram/src/main.rs:252:58:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

this can actually happen.
#2906 (comment)

Summary of Changes

instead of crash when file meta is not found, we skip them and continue.

Fixes #

[brooksprumo]

[HaoranYi]

sorry to request review again.

need to format the file.

[jeffwashington]

this is fine. I'd rather it just keep running and log failing files. If you are running this while a validator is running, it could clean something away and delete it after getting the dir but before opening the file.

[HaoranYi]

Ah. Make sense. That explains when I watch this command every 2 seconds. It failed from time to time.
I push a commit to skip failed metadata.

[brooksprumo]

[jeffwashington]

lgtm