os.getenv does not raise an exception when the value is not found. This code fix…

os.getenv does not raise an exception when the value is not found. This code fix returns (LINES, COLUMNS) when the env vars are defined, (25, 80) when they are not defined. Previously, (None, None) was returned

lettuce/terminal.py

@@ -74,9 +74,6 @@ def get_terminal_size_unix():
         except:
             pass
     if not cr:
-        try:
-            cr = (os.getenv('LINES'), os.getenv('COLUMNS'))
-        except:
-            cr = (25, 80)
+        cr = (os.getenv('LINES', 25), os.getenv('COLUMNS', 80))
 
     return int(cr[1]), int(cr[0])