PDF with OutputIntent with alternative colorspace with incorrect component count validates

as reported by "a20god", copied from linked VeraPDF issue:

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The Alternate entry of the output intent's DestOutputProfile (which is not to be ignored in PDF/A-1, in contrast to PDF/A-2)

• is a device color space which violates 6.2.3.3 (DeviceCMYK vs. RGB output intent)
• does not have the same number of components as the ICC profile (4 vs. 3), see PDF Reference 1.4 Table 4.16.