Fix crash when calling tone() with frequency 0 (#520)

Avoid division by 0 when a frequency of 0 is passed to the tone() function. If a 0 is passed, noTone() is called instead.

Author: adriaanb

cores/arduino/Tone.cpp

@@ -57,6 +57,14 @@ void toneAccurateClock (uint32_t accurateSystemCoreClockFrequency)
 
 void tone (uint32_t outputPin, uint32_t frequency, uint32_t duration)
 {
+  
+  // Avoid divide by zero error by calling 'noTone' instead
+  if (frequency == 0)
+  {
+    noTone(outputPin);
+    return;
+  }
+  
   // Configure interrupt request
   NVIC_DisableIRQ(TONE_TC_IRQn);
   NVIC_ClearPendingIRQ(TONE_TC_IRQn);