Don't crash in DirectedYield16 if no other task is running.

loader/task.c

@@ -720,6 +720,9 @@ void WINAPI DirectedYield16( HTASK16 hTask )
 {
     TDB *pCurTask = TASK_GetCurrent();
 
+    if (!pCurTask) OldYield16();
+    else
+    {
         if (pCurTask->flags & TDBF_WIN32)
         {
             FIXME("called for Win32 thread (%04x)!\n", NtCurrentTeb()->teb_sel);
@@ -727,11 +730,10 @@ void WINAPI DirectedYield16( HTASK16 hTask )
         }
 
         TRACE("%04x: DirectedYield(%04x)\n", pCurTask->hSelf, hTask );
-
         pCurTask->hYieldTo = hTask;
         OldYield16();
-
         TRACE("%04x: back from DirectedYield(%04x)\n", pCurTask->hSelf, hTask );
+    }
 }
 
 /***********************************************************************