SVGs are rendered with subpixel precision. As such it can happen that
paths are rendered with less than 1px width or height and that they can
have a bounding box thinner than 1px. Due to an optimization such paths
were ignored when painting because their bounding box was incorrectly
calculated to be empty.
As a result horizontal or vertical lines inside SVGs were missing if:
* The SVG is displayed at viewbox size but the lines are defined with
less than 1px.
* The SVG contians 1px-thin lines, but is displayed at a size smaller
than viewbox size.
To prevent this, the bounding box of the path is now enlarged to contain
all pixels that are partially affected.
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