Fix rpm warning from %post script

mariadb-connector-c.spec

@@ -52,6 +52,7 @@ Development files for mariadb-connector-c.
 %cmake . \
        -DCMAKE_BUILD_TYPE=RelWithDebInfo \
        -DMYSQL_UNIX_ADDR=/var/lib/mysql/mysql.sock \
+       -DMARIADB_PORT=3306 \
        -DWITH_EXTERNAL_ZLIB=ON \
        -DCMAKE_SYSTEM_PROCESSOR="%{_arch}" \
        -DPLUGIN_INSTALL_DIR="%{_libdir}/mariadb/plugin" \
@@ -59,6 +60,11 @@ Development files for mariadb-connector-c.
        -DINSTALL_LAYOUT=RPM \
        -DWITH_SSL=OPENSSL \
 
+# Use
+#-DMARIADB_PORT=number
+#-DMARIADB_UNIX_ADDR=/path_to_socket/file.sock
+# https://jira.mariadb.org/browse/MDEV-13836
+
 # Causes build errors
 #     -DAUTH_NATIVE=DYNAMIC
 
@@ -100,9 +106,11 @@ if [ $? -eq 1 ]; then
 fi
 
 %post devel
-if [ "$(ls -A /usr/lib64/.mysql_update_tmp)" ]; then
+if [ -d "/usr/lib64/.mysql_update_tmp" ]; then
+  if [ "$(ls -A /usr/lib64/.mysql_update_tmp)" ]; then
     mv /usr/lib64/.mysql_update_tmp/* /usr/lib64/mysql
     rm -rf /usr/lib64/.mysql_update_tmp
+  fi
 fi
 
 %post -p /sbin/ldconfig