Fixed behavior of OS.set_window_resizable

Should fix #4428. 
 * Minimize button is not hidden anymore

platform/windows/os_windows.cpp

@@ -1479,7 +1479,7 @@ void OS_Windows::set_window_resizable(bool p_enabled){
 		if (p_enabled) {
 			SetWindowLongPtr(hWnd, GWL_STYLE, WS_OVERLAPPEDWINDOW | WS_VISIBLE);
 		} else {
-			SetWindowLongPtr(hWnd, GWL_STYLE, WS_CAPTION | WS_POPUPWINDOW | WS_VISIBLE);
+			SetWindowLongPtr(hWnd, GWL_STYLE, WS_CAPTION | WS_MINIMIZEBOX | WS_POPUPWINDOW | WS_VISIBLE);
 
 		}