[PATCH] remove repetitive characters in fdwhandler.sgml

Hi all,

Here is a tiny patch removing repetitive characters [if] in fdwhandler.sgml.

Page: https://github.com/postgres/postgres/blob/master/doc/src/sgml/fdwhandler.sgml

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<para>
This function should store the tuple into the provided, or clear it if if★ The characters [if] is repeated.
the row lock couldn't be obtained. The row lock type to acquire is
defined by <literal>erm-&gt;markType</literal>, which is the value
previously returned by <function>GetForeignRowMarkType</function>.
(<literal>ROW_MARK_REFERENCE</literal> means to just re-fetch the tuple
without acquiring any lock, and <literal>ROW_MARK_COPY</literal> will
never be seen by this routine.)
</para>
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Best Regards!