fix: prevent empty window title

[raggi]

If Neovim attempts to send an empty window title, it is now set to
Neovide instead, rather than the empty string.

This improves two user scenarios:

• Users who utilize assistive technologies will now always observe a
  window title by default.
• Users of window managers that rely on window titles will have improved
  integration.

The precipitating use case was using Komorebi, a tiling window manager
for Windows. Komorebi uses an empty window title as a strong signal that
the software is a hidden window, as this is a common convention on the
platform.

Updates #1553

[fredizzimo]

I don't think this should be configurable, since the configuration can already be done with title and titlestring. But I think hardcoding it to Neovide when it's empty would be ok, that way the title can also be set immediately when the window is created and not at a later time when the configuration is read.

[raggi]

I don't think this should be configurable, since the configuration can already be done with title and titlestring. But I think hardcoding it to Neovide when it's empty would be ok, that way the title can also be set immediately when the window is created and not at a later time when the configuration is read.

Done.

[Kethku]

Thanks for the fix! I noticed a similar issue recently and hadn't tracked down what was going on.