vrend: Make the compile failure path return value consistent.

It doesn't end up getting used because the sub_ctx->prog check happens
first, but let's not return a surprising truthy value from one fail
path of a bool function.

Reviewed-by: Chia-I Wu <olvaffe@gmail.com>

src/vrend_renderer.c

@@ -4672,7 +4672,7 @@ vrend_select_program(struct vrend_sub_context *sub_ctx, const struct pipe_draw_i
       struct vrend_shader *shader = sel->current;
       if (shader && !shader->is_compiled) {//shader->sel->type == PIPE_SHADER_FRAGMENT || shader->sel->type == PIPE_SHADER_GEOMETRY) {
          if (!vrend_compile_shader(sub_ctx, shader))
-            return -1;
+            return false;
       }
       if (vrend_state.use_gles && sel->sinfo.gles_use_tex_query_level)
          gles_emulate_query_texture_levels_mask |= 1 << i;