Fix updatable driver loading issue with Vulkan.

When unloading Vulkan driver, check if close() function is non-NULL
before calling it.

Bug: 349287141
Change-Id: I1e6c3c80e57dceecd41888541044807e1dab45af

Author: Rob VanReenen

vulkan/libvulkan/driver.cpp

@@ -339,10 +339,13 @@ void Hal::UnloadBuiltinDriver() {
 
     ALOGD("Unload builtin Vulkan driver.");
 
-    // Close the opened device
-    int err = hal_.dev_->common.close(
-        const_cast<struct hw_device_t*>(&hal_.dev_->common));
-    ALOG_ASSERT(!err, "hw_device_t::close() failed.");
+    if (hal_.dev_->common.close != nullptr)
+    {
+        // Close the opened device
+        int err = hal_.dev_->common.close(
+            const_cast<struct hw_device_t*>(&hal_.dev_->common));
+        ALOG_ASSERT(!err, "hw_device_t::close() failed.");
+    }
 
     // Close the opened shared library in the hw_module_t
     android_unload_sphal_library(hal_.dev_->common.module->dso);