Made the mOStream pointer a constant-pointer-to-ostream so it can't be changed in flight.

tsmanner · tsmanner · commit 378613e1814b · 2021-05-13T14:59:47.000-04:00
diff --git a/include/conditional_ostream.h b/include/conditional_ostream.h
@@ -8,7 +8,7 @@
 //
 
 struct ConditionalOStream {
-  std::ostream *mOStream { nullptr };
+  std::ostream *const mOStream { nullptr };
 
   // Explicit constructors so that implicit
   // conversion from `std::ostream &`s can't
