get_module_file_name on main thread only

Some child plug-ins start threads, causing the DLL_THREAD_ATTACH event.
Since the MULTIPLEXER has been locked on the main thread that may be
waiting for the new threads to initialize themselves, the DllMain
implementation must not try to acquire the lock on the new threads.

src/lib.rs

@@ -275,11 +275,13 @@ extern "system" fn DllMain(dll_module: HMODULE, call_reason: DWORD, _reserved: L
     const DLL_PROCESS_DETACH: DWORD = 0;
 
     match call_reason {
-        DLL_PROCESS_ATTACH | DLL_THREAD_ATTACH => {
+        DLL_PROCESS_ATTACH => {
             let mut multiplexer = MULTIPLEXER.lock().unwrap();
             multiplexer.path = get_module_file_name(dll_module).unwrap();
         }
-        DLL_THREAD_DETACH | DLL_PROCESS_DETACH => (),
+        DLL_THREAD_ATTACH => (),
+        DLL_THREAD_DETACH => (),
+        DLL_PROCESS_DETACH => (),
         _ => (),
     }