fix a crash when saving screensets after more than one context shared…

… an ID

1. a = CreateContext('Foo')
2. b = CreateContext('Foo')
3. delete a --> screenset handler of b is unregistered
4. Save screenset --> screenset handler of the now-freed a is called
5. Use-after-free!

src/context.cpp

@@ -160,7 +160,7 @@ Context::Context(const ImGuiID id, const char *label, const int userConfigFlags)
 Context::~Context()
 {
   setCurrent();
-  screenset_unregister(m_screensetID.data());
+  screenset_unregisterByParam(this);
 
   if(m_imgui->WithinFrameScope)
     endFrame(false);

src/main.cpp

@@ -73,12 +73,12 @@ static bool loadAPI(void *(*getFunc)(const char *))
     IMPORT(GetToggleCommandState),
     IMPORT(plugin_getapi),
     IMPORT(plugin_register),
-    IMPORT(realloc_cmd_ptr), // v5.26
+    IMPORT(realloc_cmd_ptr), // v5.95
     IMPORT(ReaScriptError),
     IMPORT(RecursiveCreateDirectory),
     IMPORT(RefreshToolbar),
     IMPORT(screenset_registerNew), // v4
-    IMPORT(screenset_unregister),
+    IMPORT(screenset_unregisterByParam),
     IMPORT(ViewPrefs),
 
     IMPORT(LICE_CreateBitmap),

src/window.cpp

@@ -105,7 +105,7 @@ LRESULT CALLBACK Window::proc(HWND handle, const unsigned int msg,
     break;
   case WM_DESTROY:
     RemoveProp(handle, CLASS_NAME);
-    screenset_unregister(self->m_screensetKey.data());
+    screenset_unregisterByParam(handle);
     // Disable message passing to the derived class (not available at this point)
     SetWindowLongPtr(handle, GWLP_USERDATA, 0);
     // Announce to REAPER the window is no longer going to be valid