gallium: fix dri_destroy_option_cache() when optionCache.info is NULL

gallium: fix dri_destroy_option_cache() when optionCache.info is NULL

With an Intel 855GM handled by intel_drv, there's a crash with Gallium3D
enabled DRI driver for Intel i915 (--enable-gallium-intel).
The Gallium3D driver doesn't support the 855GM as expected by
intel_drv, it failed to open the screen and give an half
initialized screen structure to dri_destroy_option_cache():
optionCache.info is NULL, so it's crashing while trying
to free array content. This patch at least fix the crash in the function.

Here's some logs of the fixed version:

[ 16274.137] LoaderOpen(/opt/mesa/lib/xorg/modules/drivers/intel_drv.so)
[ 16274.139] (II) Loading /opt/mesa/lib/xorg/modules/drivers/intel_drv.so
[ 16274.183] (II) Module intel: vendor="X.Org Foundation"
[ 16274.183]    compiled for 1.8.0, module version = 2.11.0
[ 16274.183]    Module class: X.Org Video Driver
[ 16274.183]    ABI class: X.Org Video Driver, version 7.0
[ 16274.183] (II) intel: Driver for Intel Integrated Graphics Chipsets: i810,
        i810-dc100, i810e, i815, i830M, 845G, 852GM/855GM, 865G, 915G,
        E7221 (i915), 915GM, 945G, 945GM, 945GME, Pineview GM, Pineview G,
        965G, G35, 965Q, 946GZ, 965GM, 965GME/GLE, G33, Q35, Q33, GM45,
        4 Series, G45/G43, Q45/Q43, G41, B43, Clarkdale, Arrandale
[ 16274.382] (II) intel(0): Integrated Graphics Chipset: Intel(R) 855GME
[ 16274.382] (--) intel(0): Chipset: "852GM/855GM"
[ 16276.675] (II) intel(0): [DRI2] Setup complete
[ 16276.675] (II) intel(0): [DRI2]   DRI driver: i915
debug_get_option: GALLIUM_TRACE = (null)
debug_get_bool_option: GALLIUM_RBUG = FALSE
debug_get_bool_option: INTEL_DUMP_CMD = FALSE
i915_create_screen: unknown pci id 0x3582, cannot create screen
dri_init_screen_helper: failed to create pipe_screen
[ 16276.794] (EE) AIGLX error: Calling driver entry point failed
[ 16276.794] (EE) AIGLX: reverting to software rendering
[ 16276.794] (II) AIGLX: Screen 0 is not DRI capable
[ 16276.796] (II) AIGLX: Loaded and initialized /opt/mesa/lib/dri/swrast_dri.so
[ 16276.796] (II) GLX: Initialized DRISWRAST GL provider for screen 0

Signed-off-by: Yann Droneaud <yann@droneaud.fr>
Reviewed-by: Corbin Simpson <MostAwesomeDude@gmail.com>