Windows build doc: add Graphviz to third party install list

[vovodroid]

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There is an error message problems opening map file libheif/apidoc/html/heif_8h__incl.map while running win.bat without Graphviz installed.

Add it to third party software list.

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[ilya-fedin]

That's a wrong fix, graphviz shouldn't be needed.

[vovodroid]

Probably, but after install and rerun win.bat error message gone.

[ilya-fedin]

It's still a wrong fix. It should build without graphviz installed.

[vovodroid]

There is also the same issue: Error running win.bat #27899, it was resolved by Graphviz install.

I agree that root cause could be something else.

[ilya-fedin]

The right fix for #27899 is to remove doxygen so libheif doesn't look for graphviz

[vovodroid]

Doxygen seems to be OFF in all occurrences

https://github.com/search?q=repo%3Atelegramdesktop%2Ftdesktop%20doxygen&type=code

[ilya-fedin]

Doxygen seems to be OFF in all occurrences

I'm not sure what you want to say by that. The issue you linked says

CUSTOMBUILD : error : problems opening map file C:/TBuild/Libraries/win64/libheif/apidoc/html/heif_8h__incl.map for inc
lusion in the docs! [C:\TBuild\Libraries\win64\libheif\doc_doxygen.vcxproj]