Fix assertion failure when decoding malform G4 fax image

core/fxcodec/codec/fx_codec_fax.cpp

Index: core/fxcodec/codec/fx_codec_fax.cpp
diff --git a/core/fxcodec/codec/fx_codec_fax.cpp b/core/fxcodec/codec/fx_codec_fax.cpp
index 336c35b8d4b319bb856681f098164bdc6a102be0..c121478c3c3c268ce4a10cb83e6c2f6575a83493 100644
--- a/core/fxcodec/codec/fx_codec_fax.cpp
+++ b/core/fxcodec/codec/fx_codec_fax.cpp
@@ -390,6 +390,10 @@ FX_BOOL FaxG4GetRow(const uint8_t* src_buf,
     if (a1 >= columns)
       return TRUE;
 
+    // The position of picture element must be monotonic increasing.
+    if (a0 >= a1)
+      return FALSE;
+
     a0 = a1;
     a0color = !a0color;
   }