[latexila] BuildToolDialog: avoid critical message

[Sébastien Wilmet <swilmet src gnome org>]

commit 0b628c7b35b3a5057604d06428c2ca56748658dc
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Sat Sep 13 22:52:02 2014 +0200

    BuildToolDialog: avoid critical message
    
    gtk_entry_set_text() doesn't accept a NULL text.

 src/build_tool_dialog.vala |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/src/build_tool_dialog.vala b/src/build_tool_dialog.vala
index 3b1f6b0..faa9770 100644
--- a/src/build_tool_dialog.vala
+++ b/src/build_tool_dialog.vala
@@ -432,10 +432,10 @@ public class BuildToolDialog : GLib.Object
     {
         /* Text entries */
 
-        _entry_label.text = build_tool.label;
-        _entry_desc.text = build_tool.get_description ();
-        _entry_extensions.text = build_tool.extensions;
-        _entry_files_to_open.text = build_tool.files_to_open;
+        _entry_label.text = build_tool.label ?? "";
+        _entry_desc.text = build_tool.get_description () ?? "";
+        _entry_extensions.text = build_tool.extensions ?? "";
+        _entry_files_to_open.text = build_tool.files_to_open ?? "";
 
         /* Icon */