Bug 1565515 - DecodeBinary violates contract for 0-sized binary r=asuth,ttung

Differential Revision: https://phabricator.services.mozilla.com/D37849

--HG--
extra : moz-landing-system : lando

dom/indexedDB/Key.cpp

@@ -755,6 +755,7 @@ JSObject* Key::DecodeBinary(const unsigned char*& aPos,
   }
 
   if (!size) {
+    ++aPos;
     return JS::NewArrayBuffer(aCx, 0);
   }