Set the flag 'no_enum_check' in an exception safe way

Author: angelhof

src/analyses/goto_check.cpp

@@ -1917,13 +1917,13 @@ void goto_checkt::goto_check(
     {
       const code_assignt &code_assign=to_code_assign(i.code);
 
-      // Question: I am not sure whether adding it as a class field is
-      // better than adding it as a function argument. Adding it as an
-      // argument means that it needs to be passed as a third argument
-      // to many check_rec functions that don't really need it.
-      no_enum_check = true;
-      check(code_assign.lhs());
-      no_enum_check = false;
+      // Reset the no_enum_check with the flag reset for exception
+      // safety
+      {
+        flag_resett no_enum_check_flag_resetter;
+        no_enum_check_flag_resetter.set_flag(no_enum_check, true);
+        check(code_assign.lhs());
+      }
       check(code_assign.rhs());
 
       // the LHS might invalidate any assertion