Clean up stale editor-hInstance comments, add isOwnModulePath edge tests

Drops a false claim about ReaSampler's own editor's hInstance, corrects the real reason for registering the wndproc class against our own module, and covers isOwnModulePath's separator edge cases.

src/shell/instrument/editor_platform.cpp

@@ -36,10 +36,10 @@ const std::wstring& childClassName() {
 
 // The module holding a given code address — used to resolve THIS wndProc's own module rather
 // than the parent's hInstance REAPER hands us. Registering against the parent would put the class
-// in REAPER's own module, where a second .vst3 (the other channel) sharing that hInstance could
-// collide on the (now channel-forked) name, and any lookup-by-class would resolve into the wrong
-// binary. Takes the address rather than naming wndProc directly so a free function in this
-// anonymous namespace doesn't need access to the private member.
+// in REAPER's own module while the wndproc still points into our DLL — a dangling procedure
+// pointer once our DLL unloads but REAPER's class registration outlives it. Takes the address
+// rather than naming wndProc directly so a free function in this anonymous namespace doesn't need
+// access to the private member.
 HMODULE moduleHandleFor(void* codeAddress) {
     HMODULE mod = nullptr;
     GetModuleHandleExW(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS |