EEVEE Next: Resolve motion blur intermittent rendering

Fixes issue where motion blur would not display for
certain objects intermittently due to uninitialized
parameters in the ObjectKey struct causing the
motion object map look-up to fail and for motion
parameters to be reset to default, disabling the
effect for the given objects.

Authored by Apple: Michael Parkin-White

Co-authored-by: Michael Parkin-White <mparkinwhite@apple.com>
Pull Request: https://projects.blender.org/blender/blender/pulls/117560

source/blender/draw/engines/eevee_next/eevee_sync.hh

@@ -34,15 +34,15 @@ class Instance;
 
 class ObjectKey {
   /** Hash value of the key. */
-  uint64_t hash_value_;
+  uint64_t hash_value_ = 0;
   /** Original Object or source object for duplis. */
-  Object *ob_;
+  Object *ob_ = nullptr;
   /** Original Parent object for duplis. */
-  Object *parent_;
+  Object *parent_ = nullptr;
   /** Dupli objects recursive unique identifier */
   int id_[MAX_DUPLI_RECUR];
   /** Used for particle system hair. */
-  int sub_key_;
+  int sub_key_ = 0;
 
  public:
   ObjectKey() = default;