Backport Boost::Optional::has_value() from
https://github.com/boostorg/optional/commit/5182f7f30fad87023ae5e5a4e1f660fb513fb469
needed by LibreOffice 6.4.2


Index: boost_1_66_0/boost/optional/optional.hpp
===================================================================
--- boost_1_66_0.orig/boost/optional/optional.hpp
+++ boost_1_66_0/boost/optional/optional.hpp
@@ -1334,6 +1334,7 @@ class optional
 #endif
       
     bool operator!() const BOOST_NOEXCEPT { return !this->is_initialized() ; }
+    bool has_value() const BOOST_NOEXCEPT { return this->is_initialized() ; }
     
     BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT()
 } ;