stdin read seems racy

[dsherret]

This line when reading stdin seems racy:

https://github.com/denoland/node_deno_shims/blob/bd4a83ef3fb0788541191e4a089563c63da6cd1f/packages/shim-deno/src/deno/stable/variables/std.ts#L29

I think it's possible that between the process.stdin.read(p.length) and process.stdin.read() calls that stdin could receive more bytes than are in the buffer, which would cause a RangeError.