Multithreaded OpenGL problem (Win32)

#include <windows.h>

HWND hWnd = 0;
BOOL done = FALSE;

LRESULT WinProc(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam) {
   switch (Msg) {
      
      /* Ignore paint messages */
      case WM_PAINT:
      case WM_ERASEBKGND:
         return 0;
      
      case WM_DESTROY:
         PostQuitMessage(0);
         break;
   }
   
   return DefWindowProc(hWnd, Msg, wParam, lParam);
}

/* Creates a GL context attached to the window owned
   by the other thread and paints the client area blue */

DWORD GLThread(LPVOID lpParams) {
   PIXELFORMATDESCRIPTOR pfd = {0};
   HDC hDC = GetDC(hWnd);
   HGLRC hRC = 0;
   
   /* Set absolute minimum format attributes; i.e. select default mode */
   pfd.nSize = sizeof(PIXELFORMATDESCRIPTOR);
   pfd.nVersion = 1;
   pfd.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
   pfd.iPixelType = PFD_TYPE_RGBA;
   
   SetPixelFormat(hDC, ChoosePixelFormat(hDC, &pfd), &pfd);
   
   hRC = wglCreateContext(hDC);
   wglMakeCurrent(hDC, hRC);
   
   glClearColor(0.0f, 0.0f, 1.0f, 0.0f);
   
   while (!done) {
      glClear(GL_COLOR_BUFFER_BIT);
      SwapBuffers(hDC);
      
      /* Yield to other threads */
      Sleep(0);
   }
   
   return 0;
}

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, INT nShowCmd) {
   WNDCLASSEX wcx = {0};
   HANDLE hThread = 0;
   DWORD iThread = 0;
   DWORD wait = 0;
   MSG msg = {0};
   
   wcx.cbSize = sizeof(WNDCLASSEX);
   wcx.style = CS_OWNDC | CS_VREDRAW | CS_HREDRAW;
   wcx.lpfnWindowProc = WinProc;
   wcx.hInstance = hInstance;
   wcx.lpszClassName = "MTGL";
   /* No background brush */
   
   hWnd = CreateWindowEx(WS_EX_APPWINDOW, wcx.lpszClassName, "Untitled",
      WS_OVERLAPPEDWINDOW | WS_CLIPCHILDREN | WS_CLIPSIBLINGS, 0, 0, 320,
      240, 0, 0, hInstance, 0);
   
   ShowWindow(hWnd, nShowCmd);
   
   /* Start OpenGL */
   hThread = CreateThread(0, 0, GLThread, 0, &iThread);
   
   while (!done) {
      if (GetMessage(&msg, 0, 0) > 0) {
         DispatchMessage(&msg);
      } else {
         done = TRUE;
      }
   }
   
   return (INT)msg.wParam;
}