Check for a NULL pointer in GetWindowTextA/W.

dlls/user/tests/win.c

@@ -2771,6 +2771,15 @@ void test_scroll()
     DestroyWindow( hwnd);
 }
 
+static void test_params()
+{
+    INT rc;
+
+    /* Just a param check */
+    SetLastError(0xdeadbeef);
+    rc = GetWindowText(hwndMain2, NULL, 1024);
+    ok( rc==0, "GetWindowText: rc=%d err=%ld\n",rc,GetLastError());
+}
 
 START_TEST(win)
 {
@@ -2810,6 +2819,8 @@ START_TEST(win)
     assert( hwndMain );
     assert( hwndMain2 );
 
+    test_params();
+
     test_capture_1();
     test_capture_2();
     test_capture_3(hwndMain, hwndMain2);

dlls/user/win.c

@@ -2223,6 +2223,8 @@ INT WINAPI GetWindowTextA( HWND hwnd, LPSTR lpString, INT nMaxCount )
 {
     WCHAR *buffer;
 
+    if (!lpString) return 0;
+
     if (WIN_IsCurrentProcess( hwnd ))
         return (INT)SendMessageA( hwnd, WM_GETTEXT, nMaxCount, (LPARAM)lpString );
 
@@ -2266,6 +2268,8 @@ INT WINAPI InternalGetWindowText(HWND hwnd,LPWSTR lpString,INT nMaxCount )
  */
 INT WINAPI GetWindowTextW( HWND hwnd, LPWSTR lpString, INT nMaxCount )
 {
+    if (!lpString) return 0;
+
     if (WIN_IsCurrentProcess( hwnd ))
         return (INT)SendMessageW( hwnd, WM_GETTEXT, nMaxCount, (LPARAM)lpString );