Fix issue with functions scheduled from scheduled functions

[dok-net]

Fixes #6764

Here's my take - unknowingly working in parallel to @d-a-v - on the same issue #6764.
Copy and pasted, then adapted, the code from run_scheduled_recurrent_functions

Also, extended the MCVE to end re-scheduling at one point, in order to show that the end condition still works:

#include "Arduino.h"
#include "Schedule.h"

void cp()
{
	static int c = 0;
	if ((c++ % 10000) == 0) Serial.printf(".");
	if (c < 100000) schedule_function(cp);
}

void setup()
{
	Serial.begin(115200);
	schedule_function(cp);
}

void loop()
{
	static int l = 0;
	if ((l++ % 10000) == 0) Serial.printf(":");
}

The result:

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