We had

  if (signed < unsigned - unsigned)

which had been 'fixed' to

  if (signed < (int)unsigned - unsigned)

which didn't work because the subtraction between the two unsigned
values caused the signed value to be promoted back to unsigned again.
Change that to

  if (signed < (int) (unsigned - unsigned))

which means that the signed math will be done on the unsigned ints, but
the result will properly be interpreted as being signed before doing the
compare.

https://bugzilla.gnome.org/show_bug.cgi?id=668843