[migration] fix handling of default value for boolean attributes
We can't assert that the old value is 'True' or 'False', because False
used to be stored as an empty string in pre-3.18 versions.
<?xml version="1.0" encoding="UTF-8"?>
<display window-flags="sticky, below" width="185" height="200">
<sensor id="r" module="rqlsensor"/>
<sensor id="FS" module="FontSelector,1,Sans 10 black"/>
<!-- left border -->
<group x="0" width="5" height="200" bg-uri="gfx/border-left.png"/>
<image x="10" y="0" uri="gfx/logo_erudi.png"/>
<array id="results" x="10" y="30"
watch="layout=r:layout, length=r:length">
<label id="lbls1" color="black"
on-enter="r:enter-line"
on-leave="r:leave-line"
on-click="r:click-line"
watch="value=r:result, font=FS:font0, color=r:resultbg"/>
</array>
</display>