HDFS-15743. Fix -Pdist build failure of hadoop-hdfs-native-client. (#2569)

dev-support/bin/dist-copynativelibs

@@ -164,7 +164,7 @@ fi
 
 # Windows doesn't have a LIB_DIR, everything goes into bin
 
-if [[ -d "${BIN_DIR}" ]] ; then
+if [[ -d "${BIN_DIR}" && $(ls -A "${BIN_DIR}") ]] ; then
   mkdir -p "${TARGET_BIN_DIR}"
   cd "${BIN_DIR}"  || exit 1
   ${TAR} ./* | (cd "${TARGET_BIN_DIR}"/ || exit 1; ${UNTAR})