i965: Remember to call intel_prepare_render() before blitting.
i965: Remember to call intel_prepare_render() before blitting.

Otherwise, blits to the window system buffer may cause crashes,
since dst_irb->mt may be NULL.

This code is lifted straight out of brw_blorp_framebuffer()'s
try_blorp_blit() helper.

Fixes crashes in Piglit's fbo-sys-blit on systems without BLORP.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=65919
Signed-off-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>
Reviewed-by: Ian Romanick <83437f65a0bd3859f1a0a8228c63010af80a82d4@freedesktop.org>
Reviewed-by: Chad Versace <a557f7f75bf28dc19ac99107f5cc7cd6b3fbdb1a@linux.intel.com>
Cc: "9.2" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>

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