Avoid unnecessary detaching of containers

If only a constant iterator is needed, make the container const if
possible, otherwise use cbegin() and cend() to get a constant iterator
without detaching the container.

These fixes are needed so that `auto` can deduce the correct
iterator type.

bindings/c/tag_c.cpp

@@ -259,7 +259,7 @@ void taglib_tag_free_strings()
   if(!stringManagementEnabled)
     return;
 
-  for(List<char *>::ConstIterator it = strings.begin(); it != strings.end(); ++it)
+  for(List<char *>::ConstIterator it = strings.cbegin(); it != strings.cend(); ++it)
     free(*it);
   strings.clear();
 }