Fix malloc in _imagingft.c:font_setvaraxes

[cgohlke]

Fixes possible buffer overflow.

[cgohlke]

As expected, it's easy to crash the current implementation with any input exceeding 4*sizeof(long), e.g.:

Python 3.11.0 (main, Oct 24 2022, 18:26:48) [MSC v.1933 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from PIL import ImageFont
>>> f = ImageFont.truetype('cmr10.ttf')
>>> f
<PIL.ImageFont.FreeTypeFont object at 0x0000028609BF0510>
>>> f.set_variation_by_axes([0] * 5)
Windows fatal exception: access violation

Current thread 0x0000126c (most recent call first):
  File "X:\Python311\Lib\site-packages\PIL\ImageFont.py", line 828 in set_variation_by_axes
  File "<stdin>", line 1 in <module>