QFont::Tag: optimize toString by not searching for terminating null

The compiler knows how large the array is, so pass the size and drop
the terminating null.

Change-Id: I5795c89834b8395f04d1777d737d080f19be2a21
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
(cherry picked from commit a73f10aee422bbbee22c63ff1c436cb3193938e6)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/text/qfont.h

@@ -231,9 +231,8 @@ public:
                 char((m_value & 0xff000000) >> 24),
                 char((m_value & 0x00ff0000) >> 16),
                 char((m_value & 0x0000ff00) >> 8),
-                char((m_value & 0x000000ff)),
-                0 };
-            return QByteArray(data);
+                char((m_value & 0x000000ff)) };
+            return QByteArray(data, sizeof(data));
         }
 
         static constexpr std::optional<Tag> fromValue(quint32 value) noexcept