Fix Perlin noise fuzz issue

src/core/SkValidatingReadBuffer.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmap.h"
 #include "SkErrorInternals.h"
 #include "SkValidatingReadBuffer.h"
@@ skipping 230 matching lines @@
         fFlattenableDict.set(fFlattenableDict.count() + 1, name);
     } else {
         // Read the index.  We are guaranteed that the first byte
         // is zeroed, so we must shift down a byte.
         uint32_t index = fReader.readU32() >> 8;
         if (0 == index) {
             return nullptr; // writer failed to give us the flattenable
         }
 
         SkString* namePtr = fFlattenableDict.find(index);
-        SkASSERT(namePtr);
+        if (!namePtr) {
+            return nullptr;
+        }
         name = *namePtr;
     }
 
     // Is this the type we wanted ?
     const char* cname = name.c_str();
     SkFlattenable::Type baseType;
     if (!SkFlattenable::NameToType(cname, &baseType) || (baseType != type)) {
         return nullptr;
     }
 
@@ skipping 12 matching lines @@
     size_t offset = fReader.offset();
     obj = (*factory)(*this);
     // check that we read the amount we expected
     size_t sizeRead = fReader.offset() - offset;
     this->validate(sizeRecorded == sizeRead);
     if (fError) {
         obj = nullptr;
     }
     return obj.release();
 }