Silence clang-cl -Werror,-Wunused-but-set-parameter

...in work-in-progress code (see the comments starting at
<https://gerrit.libreoffice.org/c/core/+/147023/7#message-b9f4dd2f674548b522d3d4e657ba4517af9ff333>
"editeng: split SvxLRSpaceItem into 1 class per attribute")

Change-Id: If0e85d20d9b9e5b3dee1445ee489227f57d214ce
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/150476
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

editeng/source/items/frmitems.cxx

@@ -1388,6 +1388,8 @@ bool SvxGutterRightMarginItem::QueryValue(uno::Any& /*rVal*/, sal_uInt8 nMemberI
             // SfxDispatchController_Impl::StateChanged calls this with hardcoded 0 triggering this; there used to be a MID_LR_MARGIN 0 but what type would it have?
             OSL_FAIL("unknown MemberId");
     }
+#else
+    (void) nMemberId;
 #endif
     return bRet;
 }
@@ -1406,6 +1408,8 @@ bool SvxGutterRightMarginItem::PutValue(const uno::Any& /*rVal*/, sal_uInt8 nMem
             OSL_FAIL("unknown MemberId");
             return false;
     }
+#else
+    (void) nMemberId;
 #endif
     return true;
 }