Handle errors regarding temperature threshold (#89)

If no custom threshold is set we need something to compare to.
If the custom threshold is not a valid value we need to catch ValueError.
If the custom threshold is lower than zero we need to set some value, too.
For all these cases, we use self.THRESHOLD_TEMP as value for temp_thresh.

This fixes issue #87.

s_tui/Sources/TemperatureSource.py

@@ -47,10 +47,17 @@ def __init__(self, custom_temp=None, temp_thresh=None):
 
         # Set temperature threshold if a custom one is set
         if temp_thresh is not None:
-            if int(temp_thresh) > 0:
-                self.temp_thresh = int(temp_thresh)
-                logging.debug("Updated custom threshold to " +
-                              str(self.temp_thresh))
+            try:
+                if int(temp_thresh) > 0:
+                    self.temp_thresh = int(temp_thresh)
+                    logging.debug("Updated custom threshold to " +
+                                  str(self.temp_thresh))
+                else:
+                    self.temp_thresh = self.THRESHOLD_TEMP
+            except ValueError:
+                self.temp_thresh = self.THRESHOLD_TEMP
+        else:
+            self.temp_thresh = self.THRESHOLD_TEMP
         self.update()
         logging.debug("Update is updated to " + str(self.update))