Resolves #10830

The supersample-max-depth parameter
of gimp-drawable-edit-gradient-fill
required a value between 1 and 9.
Previously this wasn't enforced, so several
scripts called it with a value of 0.

Now that it's enforced, those scripts were
broken. This fixes the calls in weave,
gradient-example, test-sphere, burn-in,
and coffee (although it has other issues)