Fixing crash found by fuzzer

src/core/SkMallocPixelRef.cpp

Index: src/core/SkMallocPixelRef.cpp
diff --git a/src/core/SkMallocPixelRef.cpp b/src/core/SkMallocPixelRef.cpp
index b65197fac852ae7e5dceb3bf4ed4764dc92cd087..927301b763c73b2ca74c7f36e7a9343e0e20e770 100644
--- a/src/core/SkMallocPixelRef.cpp
+++ b/src/core/SkMallocPixelRef.cpp
@@ -142,7 +142,7 @@ SkMallocPixelRef::SkMallocPixelRef(SkFlattenableReadBuffer& buffer)
     , fOwnPixels(true)
 {
     fRB = buffer.read32();
-    size_t size = this->info().getSafeSize(fRB);
+    size_t size = buffer.isValid() ? this->info().getSafeSize(fRB) : 0;
     if (buffer.validateAvailable(size)) {
         fStorage = sk_malloc_throw(size);
         buffer.readByteArray(fStorage, size);