[shotwell] Prevent needless string copy

[Jens Georg <jensgeorg src gnome org>]

commit 2f9ad9731ca512f888e716c7cf5e70d701dbcc51
Author: Jens Georg <mail jensge org>
Date:   Mon Mar 13 19:02:29 2017 +0100

    Prevent needless string copy
    
    Signed-off-by: Jens Georg <mail jensge org>

 src/Printing.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/Printing.vala b/src/Printing.vala
index dab4968..1c00246 100644
--- a/src/Printing.vala
+++ b/src/Printing.vala
@@ -582,7 +582,7 @@ public class CustomPrintTab : Gtk.Box {
         Value val;
         model.get_value(iter, 0, out val);
 
-        return (val.dup_string() == "-");
+        return (val.get_string() == "-");
     }
 
     private void set_content_layout(ContentLayout content_layout) {