LCL, fix can't edit new record where key field value is NULL

git-svn-id: trunk@31361 -

lcl/include/dblookup.inc

@@ -347,11 +347,14 @@ begin
     Exit;
   end;
   LinkGetBookMark;
+  try
     try
       if FListLink.DataSet.Locate(FKeyFieldNames,
         FControlLink.DataSet.FieldValues[FDataFieldNames], []) then
-      Result := FListField.AsString
+        Result := FListField.AsString;
-    else Result:= '';
+    except
+      result := '';
+    end;
   finally
     LinkGotoBookMark;
   end;