uri: use old style constructors for pqf return value

This fixes compilation errors under clang-13

uri.hpp

@@ -104,7 +104,12 @@ namespace cruft {
         pqf (void) const& {
             return {
                 m_views[PATH].begin (),
-                m_views[FRAGMENT].end ()
+                std::size_t (
+                    std::distance (
+                        m_views[PATH].begin (),
+                        m_views[FRAGMENT].end ()
+                    )
+                )
             };
         }