Don't go further and pop the stack if it's empty.

Change-Id: I27bd30ca65cf0066cd022b4b060757913ea01fed
(cherry picked from commit 3ede68e1cc879e6adbf6336eccaf88ced974b8b6)
Reviewed-on: https://gerrit.libreoffice.org/9989
Tested-by: Michael Stahl <mstahl@redhat.com>
Reviewed-by: Michael Stahl <mstahl@redhat.com>
diff --git a/sax/source/fastparser/fastparser.cxx b/sax/source/fastparser/fastparser.cxx
index 577f414..4ddbd2a 100644
--- a/sax/source/fastparser/fastparser.cxx
+++ b/sax/source/fastparser/fastparser.cxx
@@ -492,6 +492,12 @@ void Entity::characters( const OUString& sChars )

void Entity::endElement()
{
    if (maContextStack.empty())
    {
        // Malformed XML stream !?
        return;
    }

    const SaxContext& aContext = maContextStack.top();
    const Reference< XFastContextHandler >& xContext( aContext.mxContext );
    if( xContext.is() ) try