layers: Fix memtracker segfault for ill-behaved apps

Freeing object memory before destroying object resulted in a segfault.
This is illegal but shouldn't crash the layer.
diff --git a/layers/mem_tracker.cpp b/layers/mem_tracker.cpp
index a0f45bc..44fc5d9 100644
--- a/layers/mem_tracker.cpp
+++ b/layers/mem_tracker.cpp
@@ -430,6 +430,10 @@
             /* TODO: Would be nice to return the actual object type */
             log_msg(mdd(pMemObjInfo->object), VK_DBG_REPORT_INFO_BIT, (VkObjectType) 0, (*it), 0, MEMTRACK_NONE, "MEM",
                     "VK Object %p still has a reference to mem obj %p", (*it), pMemObjInfo->mem);
+
+            // Found an object referencing this memory, remove its pointer to this memobj
+            MT_OBJ_INFO *pObjInfo = get_object_info(*it);
+            pObjInfo->pMemObjInfo = NULL;
         }
         // Clear the list of hanging references
         pMemObjInfo->pObjBindings.clear();