fix: blank lines with empty statements

[clementdessoude]

What changed with this PR:

Fix line breaks in class bodies with empty statements. The calculation of separators between class member declarations was not taking account correctly of empty statements.

Example

// Input
public class Test {
  public TestField testField;;

  @Override
  public void someMethod() {}
}
// Output (v0.6.0)
public class Test {
  public TestField testField;
  @Override
  public void someMethod() {}
}

// Output after PR:
public class Test {
  public TestField testField;

  @Override
  public void someMethod() {}
}

Relative issues or prs:

Fix #356