oleaut32: Fix return value when converting from NULL interface pointers.

dlls/oleaut32/tests/vartype.c

@@ -5889,6 +5889,16 @@ static void test_IUnknownChangeTypeEx(void)
 
   lcid = MAKELCID(MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US), SORT_DEFAULT);
 
+  /* NULL IUnknown -> IDispatch */
+  V_VT(&vSrc) = VT_UNKNOWN;
+  V_UNKNOWN(&vSrc) = NULL;
+  VariantInit(&vDst);
+  V_DISPATCH(&vDst) = (void*)0xdeadbeef;
+  hres = VariantChangeTypeEx(&vDst, &vSrc, lcid, 0, VT_DISPATCH);
+  ok(hres == S_OK && V_VT(&vDst) == VT_DISPATCH && V_DISPATCH(&vDst) == NULL,
+     "change unk(src,dst): expected 0x%08x,%d,%p, got 0x%08x,%d,%p\n",
+     S_OK, VT_DISPATCH, NULL, hres, V_VT(&vDst), V_DISPATCH(&vDst));
+
   V_VT(&vSrc) = VT_UNKNOWN;
   V_UNKNOWN(&vSrc) = pu;
 
@@ -6033,6 +6043,16 @@ static void test_IDispatchChangeTypeEx(void)
 
   lcid = MAKELCID(MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US), SORT_DEFAULT);
 
+  /* NULL IDispatch -> IUnknown */
+  V_VT(&vSrc) = VT_DISPATCH;
+  V_DISPATCH(&vSrc) = NULL;
+  VariantInit(&vDst);
+  V_UNKNOWN(&vDst) = (void*)0xdeadbeef;
+  hres = VariantChangeTypeEx(&vDst, &vSrc, lcid, 0, VT_UNKNOWN);
+  ok(hres == S_OK && V_VT(&vDst) == VT_UNKNOWN && V_UNKNOWN(&vDst) == NULL,
+     "change unk(src,dst): expected 0x%08x,%d,%p, got 0x%08x,%d,%p\n",
+     S_OK, VT_UNKNOWN, NULL, hres, V_VT(&vDst), V_UNKNOWN(&vDst));
+
   V_VT(&vSrc) = VT_DISPATCH;
   V_DISPATCH(&vSrc) = pd;
 

dlls/oleaut32/variant.c

@@ -469,7 +469,10 @@ static inline HRESULT VARIANT_Coerce(VARIANTARG* pd, LCID lcid, USHORT wFlags,
     {
     case VT_DISPATCH:
       if (V_DISPATCH(ps) == NULL)
+      {
         V_UNKNOWN(pd) = NULL;
+        res = S_OK;
+      }
       else
         res = IDispatch_QueryInterface(V_DISPATCH(ps), &IID_IUnknown, (LPVOID*)&V_UNKNOWN(pd));
       break;
@@ -481,7 +484,10 @@ static inline HRESULT VARIANT_Coerce(VARIANTARG* pd, LCID lcid, USHORT wFlags,
     {
     case VT_UNKNOWN:
       if (V_UNKNOWN(ps) == NULL)
+      {
         V_DISPATCH(pd) = NULL;
+        res = S_OK;
+      }
       else
         res = IUnknown_QueryInterface(V_UNKNOWN(ps), &IID_IDispatch, (LPVOID*)&V_DISPATCH(pd));
       break;