... clicking a GimpChain.
Since commit c0c055b4, gimp_chain_button_set_active() emits the
"toggled" signal. There is no need to emit it separately from
GimpOperationTool when setting presets with
gimp_operation_tool_set_config().

In particular, since the "toggled" signal was even sent unconditionnally
here, our code was ending creating several GBinding for the same 2
adjustments, which was creating an infinite loop.