i965: Initialize inout_offset parameter to brw_search_cache().

Two callers of brw_search_cache() weren't initializing that function's
inout_offset parameter: brw_blorp_const_color_params::get_wm_prog()
and brw_blorp_const_color_params::get_wm_prog().

That's a benign problem, since the only effect of not initializing
inout_offset prior to calling brw_search_cache() is that the bit
corresponding to cache_id in brw->state.dirty.cache may not be set
reliably.  This is ok, since the cache_id's used by
brw_blorp_const_color_params::get_wm_prog() and
brw_blorp_blit_params::get_wm_prog() (BRW_BLORP_CONST_COLOR_PROG and
BRW_BLORP_BLIT_PROG, respectively) correspond to dirty bits that are
not used.

However, failing to initialize this parameter causes valgrind to
complain.  So let's go ahead and fix it to reduce valgrind noise.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=66779
glsl: Handle empty if statement encountered during loop analysis.

The is_loop_terminator() function was asserting that the following
kind of if statement could never occur:

    if (...) { } else { }

(presumably based on the assumption that such an if statement would be
eliminated by previous optimization stages).  But that isn't the
case--it's possible that previous optimization stages might simplify
more complex code down to this empty if statement, in which case it
won't be eliminated until the next time through the optimization loop.

So is_loop_terminator() needs to handle it.  Fortunately it's easy to
handle--it's not a loop terminator because it does nothing.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=64330
CC: mesa-stable@lists.freedesktop.org