corrected path splitting for mac relative paths

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@13891 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/filename.cpp

@@ -1484,7 +1484,10 @@ void wxFileName::SplitPath(const wxString& fullpathWithVolume,
             // the path equal to something like '/', not empty, for the files
             // immediately under root directory
             size_t len = posLastSlash;
-            if ( !len )
+
+            // this rule does not apply to mac since we do not start with colons (sep)
+            // except for relative paths
+            if ( !len && format != wxPATH_MAC)
                 len++;
 
             *pstrPath = fullpath.Left(len);