glsl: Initialize ir_texture member variable.

Fixes uninitialized pointer field defect reported by Coverity.

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/ir.h

@@ -1448,8 +1448,8 @@ enum ir_texture_opcode {
 class ir_texture : public ir_rvalue {
 public:
    ir_texture(enum ir_texture_opcode op)
-      : op(op), coordinate(NULL), projector(NULL), shadow_comparitor(NULL),
-        offset(NULL)
+      : op(op), sampler(NULL), coordinate(NULL), projector(NULL),
+        shadow_comparitor(NULL), offset(NULL)
    {
       this->ir_type = ir_type_texture;
    }