fix handling of permission error in the DeveloperZone dialog

[CompuCell3D]

Traceback (most recent call last): File "c:\CompuCell3D\Miniconda3\lib\site-packages\cc3d\twedit5\Plugins\CC3DCPPHelper\DevZoneDialog.py", line 56, in on_configurePB_clicked if not self.prep_build_dir(build_dir=build_dir): File "c:\CompuCell3D\Miniconda3\lib\site-packages\cc3d\twedit5\Plugins\CC3DCPPHelper\DevZoneDialog.py", line 103, in prep_build_dir shutil.rmtree(build_dir) File "c:\CompuCell3D\Miniconda3\lib\shutil.py", line 750, in rmtree return _rmtree_unsafe(path, onerror) File "c:\CompuCell3D\Miniconda3\lib\shutil.py", line 624, in _rmtree_unsafe onerror(os.rmdir, path, sys.exc_info()) File "c:\CompuCell3D\Miniconda3\lib\shutil.py", line 622, in _rmtree_unsafe os.rmdir(path) PermissionError: [WinError 32] The process cannot access the file because it is being used by another process: 'D:\\src\\CompuCell3D_dev_zone_build' "SIMULATION FINISHED"