Zero jpeg_decompress_struct before calling jpeg_calc_output_dimensions().

https://uberchromegw.corp.google.com/i/client.skia/builders/Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-Valgrind/builds/38/steps/dm/logs/stdio

(Must have been https://codereview.chromium.org/1076923002 ?)

BUG=skia:

Review URL: https://codereview.chromium.org/1094603002
diff --git a/src/codec/SkJpegCodec.cpp b/src/codec/SkJpegCodec.cpp
index 6f7af49..a4ad766 100644
--- a/src/codec/SkJpegCodec.cpp
+++ b/src/codec/SkJpegCodec.cpp
@@ -188,6 +188,7 @@
 
     // Set up a fake decompress struct in order to use libjpeg to calculate output dimensions
     jpeg_decompress_struct dinfo;
+    sk_bzero(&dinfo, sizeof(dinfo));
     dinfo.image_width = this->getInfo().width();
     dinfo.image_height = this->getInfo().height();
     dinfo.global_state = DSTATE_READY;