Restrict thermistor table range to 0C-500C

We don't care about the accuracy of very cold temperatures
or unreasonably hot ones.

configtool/thermistortablefile.py

@@ -115,11 +115,16 @@ def BetaTable(ofp, params, names, settings, finalTable):
   # Calculate actual temps for all ADC values.
   actual = dict([(x, thrm.temp(1.0 * x)) for x in range(1, int(hiadc + 1))])
 
+  # Limit ADC range to 0C to 500C
+  MIN_TEMP = 0
+  MAX_TEMP = 500
+  actual = dict([(adc,actual[adc]) for adc in actual if actual[adc] <= MAX_TEMP and actual[adc] >= MIN_TEMP])
+
   # Build a lookup table starting with the extremes.
-  lookup = dict([(x, actual[x]) for x in [1, int(hiadc)]])
 
-  A = 1
-  B = int(hiadc)
+  A = min(actual)
+  B = max(actual)
+  lookup = dict([(x, actual[x]) for x in [A,B]])
   error = dict({})
   while len(lookup) < N:
     error.update(dict([(x, abs(actual[x] - LinearTableEstimate(lookup, x)))