Clean up after longjmp in SkImageDecoder_libpng.

src/images/SkImageDecoder_libpng.cpp

Index: src/images/SkImageDecoder_libpng.cpp
diff --git a/src/images/SkImageDecoder_libpng.cpp b/src/images/SkImageDecoder_libpng.cpp
index b51ffb9ea3676799d2387cdc3283ed2472cc345d..02ba6af90a34be865e92105c4c29ade78c39bcfc 100644
--- a/src/images/SkImageDecoder_libpng.cpp
+++ b/src/images/SkImageDecoder_libpng.cpp
@@ -255,6 +255,7 @@ bool SkPNGImageDecoder::onDecodeInit(SkStream* sk_stream, png_structp *png_ptrp,
     * set up your own error handlers in the png_create_read_struct() earlier.
     */
     if (setjmp(png_jmpbuf(png_ptr))) {
+        png_destroy_read_struct(&png_ptr, &info_ptr, png_infopp_NULL);
         return false;
     }