[BUGFIX] Don't set empty from-name when sending email

If no name is specified, only an email-address, for a sender
avoid setting an empty "from"-parameter.

Change-Id: I4274fd6d227d56d81b42be549e3780a2a29e06cc
Fixes: #44484
Releases: 4.7, 6.0, 6.1
Reviewed-on: https://review.typo3.org/19875
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn