ieframe: Never pass a NULL string pointer with DISPID_STATUSTEXTCHANGE.

dlls/ieframe/navigate.c

@@ -115,7 +115,7 @@ static void set_status_text(BindStatusCallback *This, ULONG statuscode, LPCWSTR
     }
 
     V_VT(&arg) = VT_BSTR;
-    V_BSTR(&arg) = str ? SysAllocString(buffer) : NULL;
+    V_BSTR(&arg) = str ? SysAllocString(buffer) : SysAllocString(emptyW);
     TRACE("=> %s\n", debugstr_w(V_BSTR(&arg)));
 
     call_sink(This->doc_host->cps.wbe2, DISPID_STATUSTEXTCHANGE, &dispparams);

dlls/ieframe/tests/webbrowser.c

@@ -833,6 +833,7 @@ static HRESULT WINAPI WebBrowserEvents2_Invoke(IDispatch *iface, DISPID dispIdMe
         ok(pDispParams->cArgs == 1, "cArgs=%d, expected 1\n", pDispParams->cArgs);
         ok(V_VT(pDispParams->rgvarg) == VT_BSTR, "V_VT(pDispParams->rgvarg)=%d, expected VT_BSTR\n",
            V_VT(pDispParams->rgvarg));
+        ok(V_BSTR(pDispParams->rgvarg) != NULL, "V_BSTR(pDispParams->rgvarg) is NULL\n");
         /* TODO: Check text */
         break;