[locale]Fix build (clang, Debian)

- This is a follow-up to d0c205c1cc6a2ae49935c92bfd52911b9a0d43f7;
  I really don't know why static constexpr const elements that are
  not referenced by address need to be defined separately.

src/modules/locale/timezonewidget/TimeZoneImage.cpp

@@ -34,6 +34,9 @@ static_assert( TimeZoneImageList::zoneCount == ( sizeof( zoneNames ) / sizeof( z
 #define ZONE_NAME QStringLiteral( "zone" )
 
 /* static constexpr */ const int TimeZoneImageList::zoneCount;
+/* static constexpr */ const QSize TimeZoneImageList::imageSize;
+
+static_assert( TimeZoneImageList::zoneCount == 38 );
 
 TimeZoneImageList::TimeZoneImageList() {}