Allow text frames with encoding type 1 and big endian BOM to be decoded ...

...as big endian.

They're seemingly rare, but I found some v2.3 tags that used a big endian BOM, and noticed they weren't parsing correctly. Per the spec, encoding type 1 can specify a BOM with big endian.

So, added a check to see if there's a BE BOM on text frames when encoding type 1 is used, and switch it to BE if this is the case.