Ews2Case Manage "No Subject" attachment email #29

Hello,

When Attchement email has niether name nor subject case observable cannot be created.
Maybye add a test of empty string or none in workflows/objects/TempAttachment.py) before filename = slugify(filename) and put NoName.

Traceback (most recent call last):
File "synapse/workflows/Ews2Case.py", line 85, in connectEws
tempAttachment = TempAttachment(attachmentLvl1)
File "synapse/workflows/objects/TempAttachment.py", line 60, in init
self.filename = self.getFilename()
File "synapse/workflows/objects/TempAttachment.py", line 83, in getFilename
filename = slugify(filename)
File "/usr/local/lib/python3.7/site-packages/slugify/slugify.py", line 97, in slugify
text = _unicode(text, 'utf-8', 'ignore')
TypeError: decoding to str: need a bytes-like object, NoneType found