Fix default alignment on BCheckBox.

Was most readily noticeable in WebPositive's Find pane, where the
CheckBox was incorrectly top-aligned. Thanks to Humdinger for reporting.

src/kits/interface/CheckBox.cpp

@@ -468,7 +468,7 @@ BAlignment
 BCheckBox::LayoutAlignment()
 {
 	return BLayoutUtils::ComposeAlignment(ExplicitAlignment(),
-		BAlignment(B_ALIGN_LEFT, B_ALIGN_VERTICAL_UNSET));
+		BAlignment(B_ALIGN_LEFT, B_ALIGN_VERTICAL_CENTER));
 }