Symfony version(s) affected: 4.3.3

Description
This mime type definition [0] cause notice (Notice: Undefined offset: 1) here [1] because of this [2].
[0]
https://github.com/symfony/mime/blob/e543521a5566dc2be7b675f50500f4ed8feadc60/MimeTypes.php#L2439
[1]
https://github.com/symfony/mime/blob/c71b839cc39d446f14afaef771c16f221d85c331/Part/DataPart.php#L38
[2]
https://github.com/symfony/mime/blob/c71b839cc39d446f14afaef771c16f221d85c331/Part/DataPart.php#L56

The auto mime type detection pick ups the first mime type without slash and the explode function results in a 1 item length array.
You can send the mime type on the 3rd argument, but i don't think this is a best solution.
We should do a better error reporting at the explode function.

How to reproduce
DataPart::fromPath('somefile.odt');