Getting errors when adding/editing watch while script execution is not in break state

Error messages printed:
```
ERROR: ScriptDebugger::set_watch_expression: Condition ' lang->debug_get_stack_level_count() <= 0 ' is true.
   At: core\script_language.cpp:385
ERROR: There was previously a parse error:
   At: core\math\expression.cpp:2125
ERROR: There was previously a parse error:
   At: core\math\expression.cpp:2125
```