fixes Image ref in Chinese Platforms Whitepaper

[lianmakesthings]

In the Chinese translation of the platforms whitepaper, a non-existing image platforms-def.drawio.zh.png is referenced. This PR displays the English version of the image as long as the chinese version does not exist

@node

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[node]

I will check it later . Thank you. :smile:

//UPDATE I realized that when I submitted the Chinese translation previously, I did omit the image files; we actually translated the images at that time as well. Now there are 2 alternatives to try:

1. merge this PR first, and then I submit the image file via another new PR.
2. I'll submit a new PR directly to make sure it's fixed, and then I can close this PR.

[lianmakesthings]

Let's go with option 1, then there's no pressure on you to submit the translated image :)

[node]

Created new PR #648 for adding the missing picture.

[lianmakesthings]

Closed in favour of #648