Default theme: navigation/close-small drew nothing, in either variant

Both `close-small.svg` files, `line` and `filled`, held the two diagonals of the cross as bare segments, `M785 3221L799 3235` and its mirror, painted with `fill="#000000"` and no stroke. A straight segment encloses no area, so filling it paints no pixel, and `stroke` defaults to `none`: the file is valid SVG that renders as a fully transparent image, in ltk's rasteriser and in Inkscape alike. The rest of the catalogue is drawn as closed outlines, which is what lets an icon be filled and tinted without depending on a line width; this one looks like it was exported with its strokes never converted to paths. A scan of the 432 icons of the catalogue for the same pattern, no stroke and no closed subpath, turns up no other icon with the defect.
Each diagonal is now a closed shape: two parallel sides 1.5 units apart joined by a half circle at each end, the rounded ends `close.svg` has. The width is a little heavier in proportion than that icon's (2 units on a 23.6 box), since this one exists to be drawn small. The `viewBox`, each variant's own `translate` and the visual extent of the original drawing, 0.5 to 14.5, are kept: the axes are inset by the half width so the caps end where the tips of the segments were. Both diagonals are subpaths of a single path filled with the default `nonzero` rule, on purpose: the `evenodd` that `close.svg` carries would punch a hole where they overlap. `line` and `filled` share the shape, as they do for `close.svg`.
The outlines use elliptical arc commands, which no other icon of the catalogue does; they were checked by rasterising both files with Inkscape.

themes/default/icons/catalogue/filled/navigation/close-small.svg

@@ -1,6 +1,5 @@
 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 15.000 15.000" fill="none">
 <g transform="translate(-816.500 -3220.500)" fill="#000000">
-<path d="M817 3221L831 3235"/>
-<path d="M817 3235L831 3221"/>
+<path d="M817.22 3222.28L829.72 3234.78A0.75 0.75 0 0 0 830.78 3233.72L818.28 3221.22A0.75 0.75 0 0 0 817.22 3222.28ZM818.28 3234.78L830.78 3222.28A0.75 0.75 0 0 0 829.72 3221.22L817.22 3233.72A0.75 0.75 0 0 0 818.28 3234.78Z"/>
 </g>
 </svg>

themes/default/icons/catalogue/line/navigation/close-small.svg

@@ -1,6 +1,5 @@
 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 15.000 15.000" fill="none">
 <g transform="translate(-784.500 -3220.500)" fill="#000000">
-<path d="M785 3221L799 3235"/>
-<path d="M785 3235L799 3221"/>
+<path d="M785.22 3222.28L797.72 3234.78A0.75 0.75 0 0 0 798.78 3233.72L786.28 3221.22A0.75 0.75 0 0 0 785.22 3222.28ZM786.28 3234.78L798.78 3222.28A0.75 0.75 0 0 0 797.72 3221.22L785.22 3233.72A0.75 0.75 0 0 0 786.28 3234.78Z"/>
 </g>
 </svg>