Check if image width or height are zero before proceeding.

If the width of the CJBig2_Image is set to 0 then the stride_pixels will be
zero and when we divide we'll get a floating point exception.

If the width or height are zero then we can exit early without proceeding with
the rest of the constructor.

BUG=chromium:635008

Review-Url: https://codereview.chromium.org/2222843004

core/fxcodec/jbig2/JBig2_Image.cpp

diff --git a/core/fxcodec/jbig2/JBig2_Image.cpp b/core/fxcodec/jbig2/JBig2_Image.cpp
index b8cb211..2071221 100644
--- a/core/fxcodec/jbig2/JBig2_Image.cpp
+++ b/core/fxcodec/jbig2/JBig2_Image.cpp
@@ -23,7 +23,7 @@
       m_nHeight(0),
       m_nStride(0),
       m_bOwnsBuffer(true) {
-  if (w < 0 || h < 0 || w > kMaxImagePixels)
+  if (w <= 0 || h <= 0 || w > kMaxImagePixels)
     return;
 
   int32_t stride_pixels = (w + 31) & ~31;