Various changes suggested by cppcheck

- remove unused variables
- reduce the scope where it makes sense
- correct limits (did you know that strcat()'s last parameter does not
  include the \0 that is always added?)
- set some free()'d pointers to NULL

Source/Core/DolphinWX/ISOProperties.cpp

@@ -916,7 +916,6 @@ void CISOProperties::OnExtractDir(wxCommandEvent& event)
 
 void CISOProperties::OnExtractDataFromHeader(wxCommandEvent& event)
 {
-	std::vector<const DiscIO::SFileInfo *> fst;
 	DiscIO::IFileSystem *FS = NULL;
 	wxString Path = wxDirSelector(_("Choose the folder to extract to"));