mesa: use default geometry's samples when there are no attachments

Whether multisampling is turned on depends, in part, on whether
attachments are themselves multisample surfaces. However when there are
no attachments, we should rely on the default geometry for this.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/mesa/main/state.c

@@ -352,7 +352,7 @@ update_multisample(struct gl_context *ctx)
    ctx->Multisample._Enabled = GL_FALSE;
    if (ctx->Multisample.Enabled &&
        ctx->DrawBuffer &&
-       ctx->DrawBuffer->Visual.sampleBuffers)
+       _mesa_geometric_samples(ctx->DrawBuffer) > 0)
       ctx->Multisample._Enabled = GL_TRUE;
 }