Fix Perlin noise fuzz issue

src/core/SkValidatingReadBuffer.cpp

Index: src/core/SkValidatingReadBuffer.cpp
diff --git a/src/core/SkValidatingReadBuffer.cpp b/src/core/SkValidatingReadBuffer.cpp
index 277951688945d1a83969b168d1d50c8ba2ead766..2dd70706db079b6ea23dba98017915080efb1ab9 100644
--- a/src/core/SkValidatingReadBuffer.cpp
+++ b/src/core/SkValidatingReadBuffer.cpp
@@ -248,7 +248,9 @@ SkFlattenable* SkValidatingReadBuffer::readFlattenable(SkFlattenable::Type type)
         }
 
         SkString* namePtr = fFlattenableDict.find(index);
-        SkASSERT(namePtr);
+        if (!namePtr) {
+            return nullptr;
+        }
         name = *namePtr;
     }