Wrap all stream write calls with nil checks

There might be cases where config entry is invalid thus `resolvePath` will fail and stream will be nil even after a `newFileStream`. An example case is in https://github.com/crashappsec/nimutils/blob/main/src/nimutils/sinks.nim#L32 which has resulted in nil deref in some tests. Should we create a generic wrapper on all stream writes with a check for nil, throwing an exception or logging and returning if the stream is nil?