fix expanding of current file path in shared project tree

to reproduce the issue:
1) let g:EclimProjectTreeExpandPathOnOpen = 1
2) open vim in a project w/ no buffer
3) open the project tree (no dirs expand), then close it
4) edit a file more than one dir deep
5) open the project tree (file's path should be expanded)
6) close the project tree and open another file in a different dir
7) open the project tree (new file's path should also be expanded)