Fix #73642: ftp_mkdir make an error if folder exist

reference/ftp/functions/ftp-mkdir.xml

@@ -45,6 +45,15 @@
    Returns the newly created directory name on success or &false; on error.
   </para>
  </refsect1>
+
+ <refsect1 role="errors">
+  &reftitle.errors;
+  <simpara>
+   Emits an <constant>E_WARNING</constant> level error if the directory
+   already exists or the relevant permissions prevent creating the directory.
+  </simpara>
+ </refsect1>
+
  <refsect1 role="examples">
   &reftitle.examples;
   <para>