[Mesa-dev] draw_buffer_enum_to_bitmask returns wrong answer in certain cases

[Gurchetan Singh]

When the draw_buffer_enum_to_bitmask function is called while Mesa is
in it's meta state, the wrong GLbitfield is returned sometimes for
OpenGL ES contexts.  This is because the _mesa_meta_begin function
makes the ctx->API always equal to the desktop GL during the meta
state.

In the case of GL_BACK, the _mesa_is_gles(ctx) function is checked
when returning the enum.  This check evaluates to false during the
meta state, even on mobile devices.

Any suggestions on how to fix this?