Ignore a malformed viewBox instead of raising TypeError

[eeshsaxena]

An SVG with a viewBox that isn't four numbers crashes svg2rlg:

import io
from svglib.svglib import svg2rlg
svg2rlg(io.StringIO('<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100"><rect width="5" height="5"/></svg>'))
# TypeError: Box.__new__() missing 1 required positional argument: 'height'

get_box does values = [float(v) for v in view_box.split()] then return Box(*values) without checking the count, so a viewBox with the wrong number of values raises TypeError (and a non-numeric one raises ValueError). Per the SVG spec an invalid viewBox is ignored, so I fall through to the existing width/height fallback when it doesn't parse to exactly four numbers. Valid viewBoxes are unaffected.

Added a test; it raises TypeError on main and passes with the change, and the rest of test_basic.py still passes. Found it by fuzzing svg2rlg with mutated SVG.

[github-actions]

Thank you for making your first pull request! Your contribution to svglib is highly appreciated!

[deeplook]

Thanks for the fix and tests!