[gtk-mac-bundler] Make the launcher_script element behave the way described in the example bundle.

[John Ralls <jralls src gnome org>]

commit a3bd48d83a3dce4e47dfefb23bf3f49e17cdc75e
Author: John Ralls <jralls ceridwen us>
Date:   Sat Aug 13 17:56:46 2016 -0700

    Make the launcher_script element behave the way described in the example bundle.

 bundler/project.py |   15 +++++++++------
 bundler/utils.py   |    2 ++
 2 files changed, 11 insertions(+), 6 deletions(-)
---
diff --git a/bundler/project.py b/bundler/project.py
index 60f0541..c130f97 100644
--- a/bundler/project.py
+++ b/bundler/project.py
@@ -324,13 +324,16 @@ class Project:
         node = utils.node_get_element_by_tag_name(self.root, "launcher-script")
         if node:
             path = Path.from_node(node, False)
-            path.dest = "${bundle}/Contents/MacOS/${name}"
-        else:
-            # Use the default launcher.
-            launcher = os.path.join(os.path.dirname(__file__), "launcher.sh")
-            path = Path(launcher, "${bundle}/Contents/MacOS/${name}")
+            if not path.source:
+                # Use the default launcher.
+                launcher = os.path.join(os.path.dirname(__file__),
+                                        "launcher.sh")
+                path = Path(launcher, "${bundle}/Contents/MacOS/${name}")
+            else:
+                path.dest = "${bundle}/Contents/MacOS/${name}"
+            return path
 
-        return path
+        return None
 
     def get_icon_themes(self):
         themes = []
diff --git a/bundler/utils.py b/bundler/utils.py
index 76c83d1..62b5140 100644
--- a/bundler/utils.py
+++ b/bundler/utils.py
@@ -78,6 +78,8 @@ def node_get_element_by_tag_name(node, name):
 
 def node_get_string(node, default=None):
     try:
+        if node.firstChild == None:
+            return None
         return node.firstChild.data.strip()
     except:
         return default