Fix crash when changing hotkeys after detaching video

ToolTipManager's slots can outlive the windows they're for, so use
wxWeakRef to avoid trying to update the tooltip for windows that have
been destroyed.

Originally committed to SVN as r6830.

aegisub/src/tooltip_manager.cpp

@@ -42,19 +42,43 @@
 
 #include <libaegisub/hotkey.h>
 
+#ifndef AGI_PRE
+#include <wx/window.h>
+#endif
+
+#include <wx/weakref.h>
+
 struct ToolTipBinding {
-	wxWindow *window;
+	wxWeakRef<wxWindow> window;
 	wxString toolTip;
 	const char *command;
 	const char *context;
 	void Update();
+
+	ToolTipBinding(wxWindow *window, wxString toolTip, const char *command, const char *context)
+	: window(window)
+	, toolTip(toolTip)
+	, command(command)
+	, context(context)
+	{
+	}
+
+	// clang doesn't like wxWeakRef's copy constructor, so use the assignment
+	// operator instead
+	ToolTipBinding(ToolTipBinding const& other)
+	: toolTip(other.toolTip)
+	, command(other.command)
+	, context(other.context)
+	{
+		window = other.window;
+	}
 };
 
 ToolTipManager::ToolTipManager() { }
 ToolTipManager::~ToolTipManager() { }
 
 void ToolTipManager::Bind(wxWindow *window, wxString tooltip, const char *context, const char *command) {
-	ToolTipBinding tip = { window, tooltip, command, context };
+	ToolTipBinding tip(window, tooltip, command, context);
 	tip.Update();
 
 	static ToolTipManager instance;
@@ -63,6 +87,8 @@ void ToolTipManager::Bind(wxWindow *window, wxString tooltip, const char *contex
 }
 
 void ToolTipBinding::Update() {
+	if (!window.get()) return;
+
 	std::vector<std::string> hotkeys = hotkey::get_hotkey_strs(context, command);
 
 	std::string str;

aegisub/src/tooltip_manager.h

@@ -36,15 +36,13 @@
 
 #ifndef AGI_PRE
 #include <list>
-#include <vector>
-
-#include <wx/arrstr.h>
-#include <wx/string.h>
-#include <wx/window.h>
 #endif
 
 struct ToolTipBinding;
 
+class wxString;
+class wxWindow;
+
 /// DOCME
 /// @class ToolTipManager
 /// @brief DOCME