for for initializing wxFileName with empty string returning true from IsOk() and tests for the correct behaviour (patch 1617156)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@43992 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/filename.cpp

@@ -427,7 +427,7 @@ void wxFileName::Assign(const wxString& fullpathOrig,
     // always recognize fullpath as directory, even if it doesn't end with a
     // slash
     wxString fullpath = fullpathOrig;
-    if ( !wxEndsWithPathSeparator(fullpath) )
+    if ( !fullpath.empty() && !wxEndsWithPathSeparator(fullpath) )
     {
         fullpath += GetPathSeparator(format);
     }