i965: Always intel_prepare_render() after invalidating front buffers.
i965: Always intel_prepare_render() after invalidating front buffers.

Fixes glean/texture_srgb, which hit recursive-flush prevention
assertions in vbo_exec_FlushVertices.

This probably hurts the performance of front buffer rendering, but
very few people in their right mind do front buffer rendering.

Fixes Glean's texture_srgb test.

Cc: "10.2" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>
Signed-off-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>
Acked-by: Anuj Phogat <e2026475996c48f0b97fd37e84129b3912980428@gmail.com>
Reviewed-by: Eric Anholt <96f164ad4d9b2b0dacf8ebee2bb1eeb3aa69adf1@anholt.net>

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