treemacs-create-file with point on project (not file/directory) fails

[thomassross]

Steps to reproduce:

1. Open treemacs
2. Add a project
3. With the point at the project name (not a file or directory), type c f
4. Observe the failure

Traceback:

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  file-directory-p(nil)
  treemacs--create-file/dir(t)
  treemacs-create-file()
  funcall-interactively(treemacs-create-file)
  call-interactively(treemacs-create-file nil nil)
  command-execute(treemacs-create-file)

[Alexander-Miller]

I've pushed a patch to fix this bug for all file management interactions that ask you for a location.

[thomassross]

Thank you!