message: core: add conversion from `Option<Level>` to `LevelFilter`
  Resolves a previously unreported issue where `Option<Level>` is not
  a valid `LevelFilter`.
diff: @@ -365,6 +365,13 @@ impl From<Level> for LevelFilter {
  }
  }
  +impl From<Option<Level>> for LevelFilter {
  + #[inline]
  + fn from(level: Option<Level>) -> Self {
  + Self(level)
  + }
  +}
  +
  impl Into<Option<Level>> for LevelFilter {
  #[inline]
  fn into(self) -> Option<Level> {
  @@ -819,8 +826,15 @@ mod tests {
  ];
  for (filter, level) in mapping.iter() {
  assert_eq!(filter.clone().into_level(), *level);
  - if let Some(level) = level {
  - assert_eq!(LevelFilter::from_level(level.clone()), *filter);
  + match level {
  + Some(level) => {
  + let actual: LevelFilter = level.clone().into();
  + assert_eq!(actual, *filter);
  + }
  + None => {
  + let actual: LevelFilter = None.into();
  + assert_eq!(actual, *filter);
  + }
  }
  }
  }
  