fix a couple flaky nonnull attribute ubsan warnings

Errors this should fix:
  https://uberchromegw.corp.google.com/i/client.skia/builders/Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug-ASAN/builds/3779/steps/dm/logs/stdio
  https://uberchromegw.corp.google.com/i/client.skia/builders/Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug-ASAN/builds/3779/steps/nanobench/logs/stdio

CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug-ASAN-Trybot

TBR=reed@google.com
No API changes.

BUG=skia:

Review URL: https://codereview.chromium.org/1504313005
diff --git a/src/core/SkRecordDraw.cpp b/src/core/SkRecordDraw.cpp
index 4847273..b9bf92c 100644
--- a/src/core/SkRecordDraw.cpp
+++ b/src/core/SkRecordDraw.cpp
@@ -693,7 +693,8 @@
             // Store 'saveLayer ops from enclosing picture' + drawPict op + 'ops from sub-picture'
             dst.fKeySize = fSaveLayerOpStack.count() + src.fKeySize + 1;
             dst.fKey = new int[dst.fKeySize];
-            memcpy(dst.fKey, fSaveLayerOpStack.begin(), fSaveLayerOpStack.count() * sizeof(int));
+            sk_careful_memcpy(dst.fKey, fSaveLayerOpStack.begin(),
+                              fSaveLayerOpStack.count() * sizeof(int));
             dst.fKey[fSaveLayerOpStack.count()] = fFillBounds.currentOp();
             memcpy(&dst.fKey[fSaveLayerOpStack.count()+1], src.fKey, src.fKeySize * sizeof(int));
         }