uri: use old style constructors for pqf return value

This fixes compilation errors under clang-13

uri.hpp

@@ -103,8 +103,13 @@ namespace cruft {
         std::string_view
         pqf (void) const& {
             return {
+                m_views[PATH].begin (),
+                std::size_t (
+                    std::distance (
                         m_views[PATH].begin (),
                         m_views[FRAGMENT].end ()
+                    )
+                )
             };
         }