GetCaseCorrectPathNameEx() with bCheckExistence = true doesn't support windows
share path but occasionally it doesn't return failure and returns broken result.
For example, when we call with "\\USER-PC\Users\foo" then it converts the path
to "\Users\foo". And when "\Users\foo" exists, it returns "\Users\foo". It is
caused by missing error handling of searching for file "\\USER-PC". Also similar
bug possibly occurs even for local file path. This commit fixes these bugs.

Change-Id: Idf1dd1282510d8a6810ed239a83051bb0f8e2f87
Reviewed-on: https://gerrit.libreoffice.org/4151Reviewed-by: Luboš Luňák <l.lunak@suse.cz>
Tested-by: Luboš Luňák <l.lunak@suse.cz>