wxAuiToolBar regression in recent added Create() method

[RedTide]

m_gripperVisible and m_overflowVisible are set in Init(), too early to retrieve m_windowStyle value set later in Create().
The problem can be seen also in auidemo sample: all toolbars are shown without any overflow items dropdown button.
This patch correct the issue, adding some other member variables initialization.

[vadz]

Sorry, I don't see why do we need the duplicate initialization for. We could move the initialization of the padding fields into Init() but, frankly, why bother.

I'll apply the main part of the patch, of course, thanks for fixing this!

[VZ]

(In [72913]) Use wxAUI_TB_DEFAULT_STYLE instead of 0 as default style value.

No real changes.

See #14794.

[VZ]

(In [72914]) Fix regression with wxAuiToolBar gripper and overflow members initialization.

The changes of r72785 moved m_gripperVisible and m_overflowVisible
initialization to Init() but this was too early as these fields depend on the
window style only set when it's really created, so re-initialize them to their
proper values in Create().

Closes #14794.