layers: Move call to validateCommandBuffersNotInUse inside lock

Fixes segv in CTS multithreaded command pool test

Change-Id: I80da12fd2bb6856e3c6824f17dd92f1597121a54
diff --git a/layers/core_validation.cpp b/layers/core_validation.cpp
index aa5eafb..7a2dd69 100644
--- a/layers/core_validation.cpp
+++ b/layers/core_validation.cpp
@@ -6243,9 +6243,12 @@
     }
     dev_data->commandPoolMap.erase(commandPool);
 
+
+    VkBool32 result = validateCommandBuffersNotInUse(dev_data, commandPool);
+
     loader_platform_thread_unlock_mutex(&globalLock);
 
-    if (VK_TRUE == validateCommandBuffersNotInUse(dev_data, commandPool))
+    if (result)
         return;
 
     if (!skipCall)