stopWaveform() doesn't deinit the timer if waveform had limited runtime

[dok-net]

[...]
startWaveform(GPIO, 100, 100, 200);
delay(200);
stopWaveform();
[…]

Due to code in master branch, core_esp8266_waveform.cpp, stopWaveform(uint8_t pin):

  uint32_t mask = 1<<pin;
  if (!(waveformEnabled & mask)) {
    return false; // It's not running, nothing to do here
  }

the timer keeps running even when there isn't any other waveform or the callback attached.

Fixed in #7022