Fixed SystemError clobbering libpq errors raised without SQLSTATE

Bug vivisectioned by Eric Snow
<http://archives.postgresql.org/psycopg/2011-04/msg00019.php>.

NEWS

@@ -6,6 +6,8 @@ What's new in psycopg 2.4.1
   - Don't fail connection if the client encoding is a non-normalized
     variant. Issue reported by Peter Eisentraut.
   - Correctly detect an empty query sent to the backend (ticket #46).
+  - Fixed a SystemError clobbering libpq errors raised without SQLSTATE.
+    Bug vivisectioned by Eric Snow.
   - Allow to specify --static-libpq on setup.py command line instead of
     just in 'setup.cfg'. Patch provided by Matthew Ryan (ticket #48).
 

psycopg/pqpath.c

@@ -194,6 +194,11 @@ pq_raise(connectionObject *conn, cursorObject *curs, PGresult *pgres)
     if (code != NULL) {
         exc = exception_from_sqlstate(code);
     }
+    else {
+        /* Fallback if there is no exception code (reported happening e.g.
+         * when the connection is closed). */
+        exc = DatabaseError;
+    }
 
     /* try to remove the initial "ERROR: " part from the postgresql error */
     err2 = strip_severity(err);