[Android editor] Fix issue with importing projects

[m4gr3d]

The issue was introduced by #94113:

• Prior to Make fdialog_project up to become the child of ProjectManager instead of child of ProjectDialog #94113

  • show_dialog() was invoked in ask_for_path_and_show() before _browse_project_path() and this had the side effect of updating the value of project_path to the default project path.
  • fdialog_project's current directory is then set in _browse_project_path() to the current value of project_path

• After Make fdialog_project up to become the child of ProjectManager instead of child of ProjectDialog #94113

  • project_path has a null value when used in _browse_project_path() to update fdialog_project's current directory, causing the current directory to default to the filesystem root.

The tentative fix checks whether project_path is empty, and if so uses to the default project path instead, matching the previous behavior. There are other options available (e.g: initializing project_path's value in the constructor instead) so feedback are welcome.

We could also revert the other PR, but it may be preferable to fix forward instead since reverting would reintroduce the issue it was addressing.

Fixes #94570

[Hilderin]

I tested on my Android with the artifact from this PR and the problem is fixed.

I'm not familiar with the logic for the default project path also, but the code looks good to me.

[akien-mga]

FYI @jsjtxietian @KoBeWi

[akien-mga]

Thanks!