newcodecmodel: fix priority change when compiled with clang

- clang++ std::swap works with pre-inc/dec and g++ with post so
  we use std::iter_swap and std::advance wrappers which produce
  the same results on both compilers

Change-Id: I12a2c1f3854126096d3f4ba780c4b619c5497493
Reviewed-by: Sebastien Blin <sebastien.blin@savoirfairelinux.com>

src/newcodecmodel.cpp

@@ -92,7 +92,7 @@ NewCodecModel::increasePriority(const unsigned int& codecId, bool isVideo)
         }
         while (it != codecs.end()) {
             if (it->id == codecId) {
-                std::swap(*it, *it--);
+                std::iter_swap(it, std::prev(it));
                 break;
             }
             it++;
@@ -115,7 +115,7 @@ NewCodecModel::decreasePriority(const unsigned int& codecId, bool isVideo)
         }
         while (it != codecs.end()) {
             if (it->id == codecId) {
-                std::swap(*it, *it++);
+                std::iter_swap(it, std::next(it));
                 break;
             }
             it++;