fix issue reading memo files with leading spaces

[casperhart]

Hi @tmontaigu,

I ran in to an error reading a dbase file with memo fields, so I have created this PR to fix. Changes are:

• raise error with datafusion if there is an error parsing a record. Previously these would be silently skipped, because I had assumed these cases were just empty records when they are not.
• use TrimOption::BeginEnd instead of TrimOption::End when trying to get position in memo file. The dbase file I'm using had trimmed_value similar to the following, which would not be trimmed on the left and would then throw an error when parsing:

(10) &[32, 32, 32, 32, 32, 32, 32, 32, 32, 48]

Cheers

[tmontaigu]

Thanks