FontDescription.LoadDescription throws NullReferenceException

[Nemanja Mijailovic]

FontDescription.LoadDescription throws a NullReferenceException when loading the font from the attached archive. You can run the following code to reproduce it (the path variable should contain the path to the extracted file):

FontDescription.LoadDescription(path);

Found via SharpFuzz.

[Dirk Lemstra]

Full stackrace:

System.NullReferenceException : Object reference not set to an instance of an object.
  NameTable.cs(31,0): at SixLabors.Fonts.Tables.General.NameTable.Load(BinaryReader reader)
  at SixLabors.Fonts.Tables.General.NameTable.Load(FontReader reader)
  at SixLabors.Fonts.Tables.TableLoader.Load[TTable](FontReader reader)
  at SixLabors.Fonts.FontReader.GetTable[TTableType]()
  at SixLabors.Fonts.FontDescription.LoadDescription(FontReader reader)
  at SixLabors.Fonts.FontDescription.LoadDescription(String path)

reader.GetReaderAtTablePosition(TableName) returns null and we don't check this at several places. Wonder if we should change the code here to throw an exception when header is null instead:

public virtual BinaryReader GetReaderAtTablePosition(string tableName)
{
    TableHeader header = this.GetHeader(tableName);
    return header?.CreateReader(this.stream);
}