BUG: Fixed crash when opening save dialog with node names starting with "#:"

Where # is not a drive letter, but a number, for example in case of DICOM series numbers. This commit fixes the scenario described in issue 3991, with the additional condition that the node was loaded from file.

Re 0003991

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24500 3bd1e089-480b-0410-8dfb-8563597acbee