`stdincludes.txt` not loaded when called through `PATH`

[exodustx0]

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The manual (for both v1.90 and v2) states:

When a file with [the name stdincludes.txt] exists next to the Asar executable, Asar automatically opens it and adds every line in it as an include search path [...]

This is not true if asar is called through PATH, due to argv[0] just being asar.