Added count validation in SkImageFilter::Common::unflatten()

src/core/SkImageFilter.cpp

Index: src/core/SkImageFilter.cpp
diff --git a/src/core/SkImageFilter.cpp b/src/core/SkImageFilter.cpp
index 3eb688e2c74d9848cfdd5a0028ecf159db7edfa7..11a1420dfaf2176973f4ce9cc09706ac63694c8c 100644
--- a/src/core/SkImageFilter.cpp
+++ b/src/core/SkImageFilter.cpp
@@ -44,7 +44,7 @@ bool SkImageFilter::Common::unflatten(SkReadBuffer& buffer, int expectedCount) {
     if (expectedCount < 0) {    // means the caller doesn't care how many
         expectedCount = count;
     }
-    if (!buffer.validate(count == expectedCount)) {
+    if (!buffer.validate((count == expectedCount) && (count >= 0))) {
         return false;
     }