fix open file handle if pickledb.load fails

[ThPoll]

Hi patx,

I had problems with my client when the json file was corrupt.
E.g. you simple add additional chars behind the closing curly bracket.
}sadfasdf

In this case pickledb raises an exception, but the file handle remains open.
I wanted to delete this file, but this was not possible due to open handle.
My proposal solves this issue.
Hope you like it...

Thank you,
Thomas