screenshot: Need to wrap more functions

Need to include CreateInstance, DestroyInstance
and CreateDevice in screenshot's GetInstanceProcAddr
otherwise cannot process setup correctly.
diff --git a/layers/screenshot.cpp b/layers/screenshot.cpp
index 90d5c03..7960deb 100644
--- a/layers/screenshot.cpp
+++ b/layers/screenshot.cpp
@@ -652,6 +652,8 @@
         return (void *) vkGetInstanceProcAddr;
     }
 
+    if (!strcmp(funcName, "vkDestroyInstance"))
+        return (void *) vkDestroyInstance;
     if (!strcmp(funcName, "vkCreateInstance"))
         return (void*) vkCreateInstance;
     if (!strcmp(funcName, "vkCreateDevice"))