Update pngpread.c

[amaryans]

Description:

Copying patch from commit which fixed vulnerability

Related Issue:

• If you suggest a new feature or change, discuss it first in an issue;
• If fixing a bug, there should be an issue open describing it with the steps to reproduce.

Please link the issue here.

Motivation and Context:

Why is this change required? What problem does it solve?

If it fixes an open issue (different from the previously mentioned), please link to the issue here.

Benefited Devices:

• Device: [e.g. Raspberry Pi 3 model b+]
• OS: [e.g. Linux Raspbian 10]

How Has This Been Tested?

• Please describe in detail how you tested your changes;
• Include details of your testing environment, and the tests you ran to;
• See how your change affects other areas of the code, etc.

Don't forget to tell us witch TotalCross version you are using.

Tested Devices:

• Device: [e.g. Raspberry Pi 3 model b+]
• OS: [e.g. Linux Raspbian 10]

Screenshots or videos:

If appropriate.