hwui: Add NULL pointer check in AnimatorManager::pushStaging

Fix NULL deref

```
Cmdline: com.android.systemui
pid: 2530, tid: 2589, name: RenderThread  >>> com.android.systemui <<<
uid: 10293
signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0000000000000010
Cause: null pointer dereference
    x0  b400007cbe7b8ff0  x1  0000007bf78fb9f0  x2  b400007c8c184898  x3  0000000000000001
    x4  0000007bf78faf80  x5  00000000007f5687  x6  000000001991ade0  x7  0000000000000010
    x8  0000000000000000  x9  43490de4ff9b0700  x10 b400007cbe7b8c00  x11 0000000000000002
    x12 0000000000000000  x13 000000003f800000  x14 000000003f800000  x15 0000000000000000
    x16 0000007d71724720  x17 0000007d57ccdb00  x18 0000007bf7568000  x19 b400007cbe7b8ff0
    x20 b400007cbe7b9018  x21 b400007cbe7b8ff0  x22 b400007cbe280010  x23 b400007cbe280000
    x24 7ffffffffffffff8  x25 1fffffffffffffff  x26 00000000ffffffff  x27 b400007c7e1b0da8
    x28 0000007bf78fc000  x29 0000007bf78fb7a0
    lr  0000007d67aaf330  sp  0000007bf78fb7a0  pc  0000007d67ab1590  pst 0000000020001000

backtrace:
      #00 pc 0000000000253590  /system/lib64/libhwui.so (android::uirenderer::AnimatorManager::pushStaging()+112)
      LineageOS#1 pc 000000000025132c  /system/lib64/libhwui.so (android::uirenderer::AnimationContext::runRemainingAnimations(android::uirenderer::TreeInfo&)+44)
      LineageOS#2 pc 0000000000267664  /system/lib64/libhwui.so (android::uirenderer::AnimationContextBridge::runRemainingAnimations(android::uirenderer::TreeInfo&)+36)
      LineageOS#3 pc 0000000000292720  /system/lib64/libhwui.so (android::uirenderer::renderthread::CanvasContext::prepareTree(android::uirenderer::TreeInfo&, long*, long, android::uirenderer::RenderNode*)+352)
      LineageOS#4 pc 00000000002959c8  /system/lib64/libhwui.so (std::__1::__function::__func<android::uirenderer::renderthread::DrawFrameTask::postAndWait()::$_0, std::__1::allocator<android::uirenderer::renderthread::DrawFrameTask::postAndWait()::$_0>, void ()>::operator()() (.c1671e787f244890c877724752face20)+360)
      LineageOS#5 pc 0000000000282ce4  /system/lib64/libhwui.so (android::uirenderer::WorkQueue::process()+1108)
      LineageOS#6 pc 00000000002a808c  /system/lib64/libhwui.so (android::uirenderer::renderthread::RenderThread::threadLoop()+556)
      LineageOS#7 pc 0000000000013a14  /system/lib64/libutils.so (android::Thread::_threadLoop(void*)+436)
      LineageOS#8 pc 00000000000d07ac  /apex/com.android.runtime/lib64/bionic/libc.so (__pthread_start(void*)+204)
      LineageOS#9 pc 00000000000567f0  /apex/com.android.runtime/lib64/bionic/libc.so (__start_thread+64)
```

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>

Author: songlongdaiduong

libs/hwui/AnimatorManager.cpp

@@ -77,7 +77,7 @@ void AnimatorManager::pushStaging() {
 
         // Only add new animators that are not already in the mAnimators list
         for (auto& anim : mNewAnimators) {
-            if (anim->target() != &mParent) {
+            if (anim && anim->target() != &mParent) {
                 mAnimators.push_back(std::move(anim));
             }
         }
@@ -86,12 +86,14 @@ void AnimatorManager::pushStaging() {
 
     if (mCancelAllAnimators) {
         for (auto& animator : mAnimators) {
-            animator->forceEndNow(mAnimationHandle->context());
+            if (animator)
+                animator->forceEndNow(mAnimationHandle->context());
         }
         mCancelAllAnimators = false;
     } else {
         for (auto& animator : mAnimators) {
-            animator->pushStaging(mAnimationHandle->context());
+            if (animator)
+                animator->pushStaging(mAnimationHandle->context());
         }
     }
 }