Bug1603, speculative fix: AUNBandEQ crashes Audacity...

... I can't reproduce the symptoms on my Mac, but the stack trace supplied by
Gale shows an infinite recursion overflowing the stack.

I see that at commit d1f66d768f "Updates for wx3"
by Leland, he saw the need to set a guard against infinite recursion in another
window resizing callback.  He tested that guard, but did not set it, in two
other places.  I speculate that the cycle can be entered from those other
places, bypassing where the guard was set.  So I set the guard in more places.

src/effects/audiounits/AUControl.mm

@@ -199,7 +199,7 @@ void AUControl::OnSize(wxSizeEvent & evt)
    {
       return;
    }
-   mSettingSize = true;
+   auto vr = valueRestorer( mSettingSize, true );
 
    wxSize sz = GetSize();
 
@@ -250,8 +250,6 @@ void AUControl::OnSize(wxSizeEvent & evt)
    }
 #endif
 
-   mSettingSize = false;
-
    return;
 }
 
@@ -418,6 +416,7 @@ void AUControl::CocoaViewResized()
    {
       return;
    }
+   auto vr = valueRestorer( mSettingSize, true );
 
    NSSize viewSize = [mView frame].size;
    NSSize frameSize = [mAUView frame].size;
@@ -624,7 +623,8 @@ void AUControl::CarbonViewResized()
    {
       return;
    }
-   
+   auto vr = valueRestorer( mSettingSize, true );
+
    // resize and move window
    HIRect rect;
    HIViewGetFrame(mHIView, &rect);