fixed png images rendering issues for qrcode

[Mohammadwasifbalti]

Fixed the issue #1638

Before:

Result:

[blikblum]

Great work

Please add a changelog entry

[blikblum]

Can you upload the png that triggers the error?

[Mohammadwasifbalti]

Hi
I've already updated the changelog.md entry.
The PNG was uploaded but below is the link of that png:
https://clienwh.osapps.ae/assets/images/qrcodes/NT25073071831420.png

[Mohammadwasifbalti]

I've pushed the final code for this pull request

[blikblum]

Can you look at failed tests?

[Mohammadwasifbalti]

Tests are passed

[blikblum]

I added the following code to kitchen sink example:

doc.image('../tests/images/pngsuite-palette-transparent-white.png', 100, 200)

After this PR the image looses its transparency

We should look for a fix that do not add regressions

[blikblum]

I added the offending png to repository so we can properly test.

I'm closing since the fix is not correct although is hinting where the problem lies (the current code works by accident since alphaChannel is always truthy)