log/windows: Fix missing class member initializer

This had the confusing side-effect of making some code in wesnoth.cpp
believe it was safe to prompt the user to press Enter when NOT using
--wconsole on my system, because the flag ended up with a true value by
default.

This is why you don't leave integral-type variables uninitialized, ever.

changelog.md

@@ -16,6 +16,7 @@
  ### User interface
  ### WML Engine
  ### Miscellaneous and Bug Fixes
+   * Fixed a rare issue on Windows that could result in wesnoth.exe sticking around waiting for console input after encountering an error despite not being launched with the `--wconsole` option.
 
 ## Version 1.15.6
  ### Add-ons client

src/log_windows.cpp

@@ -282,6 +282,7 @@ log_file_manager::log_file_manager(bool native_console)
 	: fn_(unique_log_filename())
 	, cur_path_()
 	, use_wincon_(console_attached())
+	, created_wincon_(false)
 {
 	DBG_LS << "Early init message\n";