Test alpha-less 10bit formats correctly in wide_color tests

[jannau]

The test for alpha for 10bit formats did not take 'EGL_ALPHA_SIZE == 0' into account. This is expected to read back as opaque. Fixes dEQP-EGL.functional.wide_color.{pbuffer,window}_888* when a 10bit format is selected. Seen when using wayland as target.

Fixes If0541906e510b3c2191a3e9ca8be3eb2529a0475

Components: EGL

Affects:

dEQP-EGL.functional.wide_color.window_888_colorspace_default dEQP-EGL.functional.wide_color.window_888_colorspace_srgb dEQP-EGL.functional.wide_color.window_888_colorspace_p3 dEQP-EGL.functional.wide_color.window_888_colorspace_p3_passthrough dEQP-EGL.functional.wide_color.pbuffer_888_colorspace_default dEQP-EGL.functional.wide_color.pbuffer_888_colorspace_srgb dEQP-EGL.functional.wide_color.pbuffer_888_colorspace_p3 dEQP-EGL.functional.wide_color.pbuffer_888_colorspace_p3_passthrough

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