fix small bug

Author: chrisruk

buildhat/serinterface.py

@@ -271,7 +271,7 @@ def runit():
                 with self.portcond[portid]:
                     self.portcond[portid].notify()
 
-            if line[1] == "." and line.strip().endswith(" V"):
+            if len(line) >= 5 and line[1] == "." and line.strip().endswith(" V"):
                 vin = float(line.strip().split(" ")[0])
                 self.vin = vin
                 with self.vincond: