arb_direct_state_access: fix stencil usage in gettextureimage-formats
STENCIL_INDEX8 and RGBA are not compatible formats, and the former also isn't compatible with GL_FLOAT, so add special casing here
fixes mesa#5174
STENCIL_INDEX8 and RGBA are not compatible formats, and the former also isn't compatible with GL_FLOAT, so add special casing here
fixes mesa#5174