Don't run dead code removal when in calc mode. Add TODO item.

Running 'main.py -O expr' without disabling DCR led to an immediate crash, due to it trying to access the default state.

lslopt/lsldeadcode.py

@@ -475,6 +475,14 @@ class deadcode(object):
         # sophisticated (yet).
 
         # TODO: Inlining of functions that are a single 'return' line.
+        # TODO: Remove empty events if they are side effect-free.
+        # Note that e.g. touch/* events are not SEF, because their presence
+        # causes the hand to be shown, so we need a list of SEF events.
+
+        if lslfuncs.lslcommon.IsCalc:
+            # Do nothing if in calculator mode (there's no default event
+            # and it crashes without this)
+            return
 
         statedef = self.tree[self.symtab[0]['default']['Loc']]
         assert statedef['nt'] == 'STDEF' and statedef['name'] == 'default'