cid#1700595: silence Unchecked return value

Change-Id: I68a2ed40de7b41f3c1704e0f149d555bde82919e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/210282
Reviewed-by: Xisco Fauli <xiscofauli@libreoffice.org>
Tested-by: Jenkins

oox/source/crypto/AgileEngine.cxx

@@ -324,7 +324,7 @@ bool generateBytes(std::vector<sal_uInt8> & rBytes, sal_Int32 nSize)
 
     size_t nMax = std::min(rBytes.size(), size_t(nSize));
 
-    rtl_random_getBytes(nullptr, rBytes.data(), nMax);
+    (void)rtl_random_getBytes(nullptr, rBytes.data(), nMax);
 
     return true;
 }