HdySearchBar has extra padding on the sides with show-close-button=false

To reproduce in libhandy demo, set show-close-button=false on the search bar and linear-growth-width to something larger, like 400px, on HdyColumn in GtkInspector.

Here's the same thing in Games, but with spacing on tool_box box set to 0.

That spacing is required when there is a close button, so that the entry isn't directly touching it. But when the close button is not shown, I wonder if it should just be 0px.