GUI2/Modeless Dialog: minor cleanup, implement a TODO

* Use a unique_ptr for the window member.
* Made use of the new remove_from_window_stack function (its impl was copied from this code)
* Only attempt ows removal if window display mode is modeless (since if mode is tooltip, no
  ptr was added to the list anyway.

# Conflicts:
#	src/gui/dialogs/modeless_dialog.cpp

src/gui/dialogs/modeless_dialog.cpp

@@ -43,14 +43,14 @@ void modeless_dialog::show(CVideo& video,
 
 	hide();
 
-	window_ = build_window(video);
+	window_.reset(build_window(video));
 
 	post_build(*window_);
 
 	pre_show(*window_);
 
 	if(allow_interaction) {
-		open_window_stack.push_back(window_);
+		open_window_stack.push_back(window_.get());
 		window_->show_non_modal();
 	} else {
 		window_->show_tooltip(/*auto_close_time*/);
@@ -60,19 +60,13 @@ void modeless_dialog::show(CVideo& video,
 void modeless_dialog::hide()
 {
 	if(window_) {
-		// Possible TODO: Only run through this loop if the window's show_mode_ == modal
-		// (For some reason, non-modal windows still have show_mode_ = modal.)
 		// Don't bother if show_mode_ == tooltip, because in that case we didn't add it anyway.
-		for(auto iter = open_window_stack.rbegin(); iter != open_window_stack.rend(); iter++) {
-			if(*iter == window_) {
-				open_window_stack.erase(std::next(iter).base());
-				break;
-			}
+		if(window_->mode() == window::modeless) {
+			remove_from_window_stack(window_.get());
 		}
+
 		window_->undraw();
-		delete window_;
-		window_ = nullptr;
-	}
+		window_.reset(nullptr);	}
 }
 
 window* modeless_dialog::build_window(CVideo& video) const

src/gui/dialogs/modeless_dialog.hpp

@@ -14,6 +14,7 @@
 
 #pragma once
 
+#include <memory>
 #include <string>
 
 class CVideo;
@@ -84,7 +85,7 @@ class modeless_dialog
 
 private:
 	/** The window, used in show. */
-	window* window_;
+	std::unique_ptr<window> window_;
 
 	/** The id of the window to build. */
 	virtual const std::string& window_id() const = 0;