fix crash on init caused by the previous change (2/2)

fand.py

@@ -49,8 +49,12 @@ class PWM:
 		# acquire a duty cycle file descriptor
 		self.f_dc = open(self.ch_base + "duty_cycle", "w")
 		
-		# set 0 duty cycle so period can be freely set
-		self.set_duty_cycle(0)
+		# Set 0 duty cycle so period can be freely set even if the channel was used before.
+		# This may fail: ignore.
+		try:
+			self.set_duty_cycle(0)
+		except OSError:
+			pass
 		
 		# set period & polarity
 		with open(self.ch_base + "period", "w") as f: