Fix crash on macOS.

Milestone

https://github.com/tutao/tutanota/milestone/463?closed=1

Asset Checksums (SHA256)

tutanota-desktop-linux.AppImage:
afdfd2a3dc072e21bd6d847fc68f0d4b658196be1363d2d60b8e375a1bc8e809

tutanota-desktop-win.exe:
24c578104ac2b96f7063a5180579060a182c5825a7bcd44e3b80936fe9533903

tutanota-desktop-mac.dmg:
3823072b759db337f6fd948dd3c8cc0fd9fe2787faf736a3b34f5c705eb82db9