Fix FTBFS with older lucene versions

(cherry picked from commit 5fc26b8a59)

clucene.m4

@@ -48,6 +48,8 @@ if test "x$ac_cv_clucene_libdir" = "xNO"; then
   if test "x$ac_cv_clucene2_libdir" = "xNO"; then
     AC_MSG_ERROR(CLucene library not found. Try to use configure with --with-clucene-dir=/path/to/clucene);
   fi
+else
+  ac_cv_clucene2_libdir="NO"
 fi
 
 if test "x$ac_static_clucene" = "xYES"; then