Some Exception Handling and change value from DOI status from DOI table

dspace/etc/postgres/database_schema.sql

@@ -495,7 +495,7 @@ CREATE TABLE Doi
   doi              VARCHAR(256) UNIQUE,
   resource_type_id INTEGER,
   resource_id      INTEGER,
-  status           VARCHAR(20)
+  status           INTEGER
 );
 
 -- index by handle, commonly looked up