st/mesa: check for out-of-memory in st_DrawPixels()

st/mesa: check for out-of-memory in st_DrawPixels()

Before, if make_texture() or st_create_texture_sampler_view() failed
we silently no-op'd the glDrawPixels.  Now, set GL_OUT_OF_MEMORY.
This also allows us to un-nest a bunch of code.

v2: also check if allocation of sv[1] fails, per Jose.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>