Guess png dimention by file header

[jj1uzh]

Current version guesses PNG icons of some applications (e.g. Slack Desktop) to have size 1x1 because they are not in *x* directories.
Guess the size of such icons by PNG header.

[sagb]

I tried to avoid reading icon content at startup, because it possibly may cause fatal delay in some cases, for example, when /usr or home mounted over nfs.
Instead, inspectIconMeta is supposed to set 1x1 to indicate unknown size. Then, selection procedure will choose this icon if no other icons are found. Then, during runtime, only if some window match this icon, loadIconContentPNG actually reads the file.
Is this approach broken?

[martinlowet]

Is this approach broken?

It sounds good, however it currently doesn't seem to work, at least not with vscodium, which stores it's icon at /usr/share/pixmaps/vscodium.png. With this PR the problem disappears.

[sagb]

So, why didn't my approach work? Perhaps you had other icons for VSCodium, which AltTab chose instead of the desired one?