handle when getTermCols returns 0

exe/Options.idr

@@ -40,6 +40,12 @@ record Options where
 %name Options opts
 %runElab derive "Options" [Show]
 
+export
+defaultWidth : IO Nat
+defaultWidth = do
+  w <- cast {to = Nat} <$> getTermCols
+  pure $ if w == 0 then 80 else w
+
 export
 defaultOpts : IO Options
 defaultOpts = pure $ MkOpts {
@@ -47,7 +53,7 @@ defaultOpts = pure $ MkOpts {
   outFile = Console,
   until   = Nothing,
   flavor  = Unicode,
-  width   = cast !getTermCols,
+  width   = !defaultWidth,
   include = ["."]
 }