cid#1700585: silence Unchecked return value

Change-Id: I820fd0ea45466757507751130e99e2c5281adb05
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/210277
Tested-by: Jenkins
Reviewed-by: Xisco Fauli <xiscofauli@libreoffice.org>

vcl/source/pdf/PDFEncryptorR6.cxx

@@ -41,7 +41,7 @@ void generateBytes(std::vector<sal_uInt8>& rBytes, size_t nSize)
     if (rBytes.empty())
         return;
 
-    rtl_random_getBytes(nullptr, rBytes.data(), rBytes.size());
+    (void)rtl_random_getBytes(nullptr, rBytes.data(), rBytes.size());
 }
 
 } // end anonymous