function onWalk( error ) {
		if ( FLG ) {
			// Stop any further processing if currently in an error state...
			return;
		}
		if ( error ) {
			debug( 'Encountered an error when walking module dependency. Error: %s', error.message );
			FLG = true;
			return clbk( error );
		}
		count += 1;
		debug( 'Walked %d of %d module dependencies...', count, total );
		if ( count === total ) {
			debug( 'Walked all module dependencies.' );
			return clbk();
		}
	}
Callback invoked after walking a module dependency.

@private
@param {(Error|null)} error - error object
@returns {void}