comctl32: improve GUI error messages

[Austin English]

Requested by Focht. Fixes http://bugs.winehq.org/show_bug.cgi?id=34850

-- 
-Austin
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diff --git a/dlls/comctl32/commctrl.c b/dlls/comctl32/commctrl.c
index d2ad28f..236ba08 100644
--- a/dlls/comctl32/commctrl.c
+++ b/dlls/comctl32/commctrl.c
@@ -1628,7 +1628,7 @@ HRESULT WINAPI TaskDialogIndirect(const TASKDIALOGCONFIG *pTaskConfig, int *pnBu
     else
     if (pTaskConfig->dwCommonButtons & TDCBF_OK_BUTTON)
         uType |= MB_OK;
-    ret = MessageBoxW(pTaskConfig->hwndParent, pTaskConfig->pszMainInstruction,
+    ret = MessageBoxW(pTaskConfig->hwndParent, pTaskConfig->pszContent,
                       pTaskConfig->pszWindowTitle, uType);
     FIXME("dwCommonButtons=%x uType=%x ret=%x\n", pTaskConfig->dwCommonButtons, uType, ret);