fix milesburton#143 divide by zero

Author: RobTillaart

DallasTemperature.cpp

@@ -535,7 +535,7 @@ int16_t DallasTemperature::calculateTemperature(const uint8_t* deviceAddress,
 	 See - http://myarduinotoy.blogspot.co.uk/2013/02/12bit-result-from-ds18s20.html
 	 */
 
-	if (deviceAddress[0] == DS18S20MODEL) {
+	if ((deviceAddress[0] == DS18S20MODEL) && (scratchPad[COUNT_PER_C] != 0)) {
 		fpTemperature = ((fpTemperature & 0xfff0) << 3) - 32
 				+ (((scratchPad[COUNT_PER_C] - scratchPad[COUNT_REMAIN]) << 7)
 						/ scratchPad[COUNT_PER_C]);