i965/vs: Fix NULL pointer dereference in pre-Gen6 push constant loading.

According to the comment, we need to load /some/ push constants on
pre-Gen6 hardware or the GPU will hang.  The existing code set these
bogus parameters to NULL pointers; unfortunately, the code in
brw_curbe.c that loads them dereferences those pointers.  So, change
them to be pointers to an actual floating point value of 0.0.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>

src/mesa/drivers/dri/i965/brw_vec4_emit.cpp

@@ -117,8 +117,8 @@ vec4_visitor::setup_uniforms(int reg)
 
       for (unsigned int i = 0; i < 4; i++) {
 	 unsigned int slot = this->uniforms * 4 + i;
-
-	 c->prog_data.param[slot] = NULL;
+	 static float zero = 0.0;
+	 c->prog_data.param[slot] = &zero;
       }
 
       this->uniforms++;