Suppress warning: instance variable @name_to_tdo not initialized.

ChangeLog

+2016-03-27  Kubo Takehiro  <kubo@jiubao.org>
+	* lib/oci8/object.rb: Suppress warning: instance variable
+	    @name_to_tdo not initialized.
+
 2016-03-27  Kubo Takehiro  <kubo@jiubao.org>
 	* ext/oci8/apiwrap.yml, ext/oci8/metadata.c, ext/oci8/object.c,
 	  ext/oci8/oci8.h, lib/oci8/object.rb, test/setup_test_object.sql,

lib/oci8/object.rb

@@ -78,7 +78,8 @@ EOS
   #
   # @private
   def get_tdo_by_typename(typename)
-    tdo = @name_to_tdo && @name_to_tdo[typename]
+    @name_to_tdo ||= {}
+    tdo = @name_to_tdo[typename]
     return tdo if tdo
 
     metadata = describe_any(typename)