Fix arithmetic overflow in oiio_bufinfo (Python interop)

[jessey-git]

Description

When an incoming 1-dimensional, buffer-like, object was used in Python, the corresponding check inside OIIO would overflow if its length exceeded a signed 32bit value.

An error similar to Pixel data array error: Python array shape is [2304000000] but expecting h=24000, w=24000, ch=4 would be raised.

I modified a few similar calculations and tried to follow the predominant pattern already used.

Tests

Tested using the following snippet which would previously fail:

import OpenImageIO as oiio
import numpy as np

filename = "t:/foo.png"
xres = 24000
yres = 24000
channels = 4  # RGB
pixels = np.zeros(xres * yres * channels, dtype=np.uint8)

spec = oiio.ImageSpec(xres, yres, channels, "uint8")
image = oiio.ImageOutput.create(filename)
image.open(filename, spec)
if not image.write_image(pixels):
    print("error = ", image.geterror())
image.close()

Checklist:

• I have read the contribution guidelines.
• If this is more extensive than a small change to existing code, I
  have previously submitted a Contributor License Agreement
  (individual, and if there is any way my
  employers might think my programming belongs to them, then also
  corporate).
• I have updated the documentation, if applicable.
• I have ensured that the change is tested somewhere in the testsuite
  (adding new test cases if necessary).
• My code follows the prevailing code style of this project.

[lgritz]

Good catch, thanks