perf scripts python: exported-sql-viewer.py: Hide Call Graph option if no calls table

The Call Graph depends on the calls table which is optional when exporting
data, so hide the Call Graph option if there is no calls table.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/scripts/python/exported-sql-viewer.py

@@ -1786,6 +1786,16 @@ def GetEventList(db):
 		events.append(query.value(0))
 	return events
 
+# Is a table selectable
+
+def IsSelectable(db, table):
+	query = QSqlQuery(db)
+	try:
+		QueryExec(query, "SELECT * FROM " + table + " LIMIT 1")
+	except:
+		return False
+	return True
+
 # SQL data preparation
 
 def SQLTableDataPrep(query, count):
@@ -2298,7 +2308,8 @@ class MainWindow(QMainWindow):
 		edit_menu.addAction(CreateAction("&Enlarge Font", "Make text bigger", self.EnlargeFont, self, [QKeySequence("Ctrl++")]))
 
 		reports_menu = menu.addMenu("&Reports")
-		reports_menu.addAction(CreateAction("Context-Sensitive Call &Graph", "Create a new window containing a context-sensitive call graph", self.NewCallGraph, self))
+		if IsSelectable(glb.db, "calls"):
+			reports_menu.addAction(CreateAction("Context-Sensitive Call &Graph", "Create a new window containing a context-sensitive call graph", self.NewCallGraph, self))
 
 		self.EventMenu(GetEventList(glb.db), reports_menu)