gtk_tree_model_filter_row_deleted: don't emit signals too early

gtk_tree_model_filter_row_deleted: don't emit signals too early

gtk_tree_model_filter_row_deleted was emitting ::row-deleted while
the internal state of the model was still in disarray, causing
segfaults e.g. when mapping the file chooser with accessibility
turned on. This is just a bandaid fix, and doesn't try address
any of the deeper problems of the filter model code.

I did take the time to reduce rampant variable shadowing in that
function, though.