Baking does not handle upstream nodename connections

[bernardkwok]

e.g. The follow bakes no images.

<?xml version="1.0"?>
<materialx version="1.37">
  <texcoord name="texcoord" type="vector2" xpos="10" ypos="241" />
  <multiply name="multiply" type="float" xpos="620" ypos="71">
    <input name="in1" type="float" nodename="constant"  />
    <input name="in2" type="float" nodename="swizzle"  />
  </multiply>
  <multiply name="multiply1" type="float" xpos="620" ypos="290">
    <input name="in1" type="float" nodename="constant"  />
    <input name="in2" type="float" nodename="swizzle1"  />
  </multiply>
  <swizzle name="swizzle" type="float" xpos="315" ypos="10">
    <input name="in" type="vector2" nodename="texcoord"  />
  </swizzle>
  <swizzle name="swizzle1" type="float" xpos="315" ypos="424">
    <input name="in" type="vector2" nodename="texcoord"  />
    <input name="channels" type="string" uniform="true" value="y"  />
  </swizzle>
  <constant name="constant" type="float" xpos="315" ypos="229">
    <input name="value" type="float" uniform="true" value="10"  />
  </constant>
  <floor name="floor" type="float" xpos="925" ypos="248">
    <input name="in" type="float" nodename="multiply1"  />
  </floor>
  <floor name="floor1" type="float" xpos="925" ypos="53">
    <input name="in" type="float" nodename="multiply"  />
  </floor>
  <add name="add" type="float" xpos="1230" ypos="109">
    <input name="in1" type="float" nodename="floor1"  />
    <input name="in2" type="float" nodename="floor"  />
  </add>
  <modulo name="modulo" type="float" xpos="1535" ypos="79">
    <input name="in1" type="float" nodename="add"  />
    <input name="in2" type="float" value="2"  />
  </modulo>
  <standard_surface name="standard_surface" type="surfaceshader" version="1.0.1" xpos="1840" ypos="49">
    <input name="base" type="float" nodename="modulo"  />
  </standard_surface>
  <surfacematerial name="surfacematerial" type="material" xpos="2138.76" ypos="164.286">
    <input name="surfaceshader" type="surfaceshader" nodename="standard_surface"  />
    <input name="displacementshader" type="displacementshader" value=""  />
  </surfacematerial>
</materialx>