[tracker] SPARQL: Fix context handling for EXISTS and NOT EXISTS

[Jürg Billeter <juergbi src gnome org>]

commit b2cd166aa668de7f31dc2c7f88f2e4d1960ed3e3
Author: Jürg Billeter <j bitron ch>
Date:   Wed Oct 13 16:38:31 2010 +0200

    SPARQL: Fix context handling for EXISTS and NOT EXISTS

 src/libtracker-data/tracker-sparql-pattern.vala |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/src/libtracker-data/tracker-sparql-pattern.vala b/src/libtracker-data/tracker-sparql-pattern.vala
index 051e1e2..fc62abf 100644
--- a/src/libtracker-data/tracker-sparql-pattern.vala
+++ b/src/libtracker-data/tracker-sparql-pattern.vala
@@ -461,6 +461,8 @@ class Tracker.Sparql.Pattern : Object {
 		sql.append (" FROM (");
 		sql.append (pattern_sql.str);
 		sql.append (")");
+
+		context = context.parent_context;
 	}
 
 	internal string parse_var_or_term (StringBuilder? sql, out bool is_var) throws Sparql.Error {