fix SphinxSE to not leave Sphinx_error status variable uninitialized

mysql-test/suite/sphinx/sphinx.result

@@ -48,7 +48,7 @@ SET optimizer_switch=@save_optimizer_switch;
 drop table ts;
 show status like "sphinx_error%";
 Variable_name	Value
-Sphinx_error	OFF
+Sphinx_error	
 show status like "sphinx_total%";
 Variable_name	Value
 Sphinx_total	2

storage/sphinx/ha_sphinx.cc

@@ -3575,11 +3575,13 @@ int sphinx_showfunc_words ( THD * thd, SHOW_VAR * out, char * sBuffer )
 int sphinx_showfunc_error ( THD * thd, SHOW_VAR * out, char * )
 {
 	CSphSEStats * pStats = sphinx_get_stats ( thd, out );
+	out->type = SHOW_CHAR;
 	if ( pStats && pStats->m_bLastError )
 	{
-		out->type = SHOW_CHAR;
 		out->value = pStats->m_sLastMessage;
 	}
+        else
+		out->value = (char*)"";
 	return 0;
 }