anv: avoid segmentation fault due to vk_error()

vk_error() is a macro that calls __vk_errorf() with instance == NULL.

Then, __vk_errorf() passes a pointer to instance->debug_report_callbacks
to vk_debug_error(), which segfaults as this pointer is invalid but not
NULL.

Fixes: e5b1bd6ab8 "vulkan: move anv VK_EXT_debug_report implementation to common code."

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>

src/intel/vulkan/anv_util.c

@@ -99,6 +99,7 @@ __vk_errorf(struct anv_instance *instance, const void *object,
       snprintf(report, sizeof(report), "%s:%d: %s", file, line, error_str);
    }
 
+   if (instance) {
       vk_debug_report(&instance->debug_report_callbacks,
                       VK_DEBUG_REPORT_ERROR_BIT_EXT,
                       type,
@@ -107,6 +108,7 @@ __vk_errorf(struct anv_instance *instance, const void *object,
                       0,
                       "anv",
                       report);
+   }
 
    intel_loge("%s", report);