Part: Don't cast time_t to a potentially 32-bit type

Coverity (and possibly other static analyzers) detect when we attempt to use a time_t as what might be a 32-bit value, warning about Y2K38 safety. It is irrelevant in this case, but make the change to avoid the warning (so it doesn't hide any real problems).

src/Mod/Part/App/Geometry.cpp

@@ -469,7 +469,7 @@ void Geometry::createNewTag()
     boost::lock_guard<boost::mutex> guard(random_number_mutex);
 
     if (!seeded) {
-        ran.seed(static_cast<unsigned int>(std::time(nullptr)));
+        ran.seed(static_cast<std::uint64_t>(std::time(nullptr)));
         seeded = true;
     }
     static boost::uuids::basic_random_generator<boost::mt19937> gen(&ran);