Scripts: Handle "nothing installed" case gracefully for plugin builds

When (temporarily) turning off the QmlDesigner build, the separate
QmlDesigner plugin repository build results in nothing being installed.
The 7zip call and signing code then fails if the installation directory
isn't even created as a consequence.

Change-Id: I14cc9504b6a5d653ab94845423e266d2cb8caf42
Reviewed-by: David Schulz <david.schulz@qt.io>

scripts/build_plugin.py

@@ -142,6 +142,8 @@ def build(args, paths):
                                  paths.build)
 
 def package(args, paths):
+    if not os.path.exists(paths.install):
+        os.makedirs(paths.install)
     if not os.path.exists(paths.result):
         os.makedirs(paths.result)
     if common.is_windows_platform() and args.sign_command:
@@ -165,14 +167,19 @@ def package(args, paths):
         if os.environ.get('SIGNING_IDENTITY'):
             signed_install_path = paths.install + '-signed'
             common.copytree(paths.install, signed_install_path, symlinks=True)
+            zippattern = None
+            if os.path.exists(signed_install_path):
                 apps = [d for d in os.listdir(signed_install_path) if d.endswith('.app')]
                 if apps:
-                app = apps[0]
+                    zippattern = apps[0]
-                common.conditional_sign_recursive(os.path.join(signed_install_path, app),
+            if not zippattern:
+                os.makedirs(signed_install_path)  # if nothing was installed
+                zippattern = '*'
+            common.conditional_sign_recursive(signed_install_path,
                                               lambda ff: ff.endswith('.dylib'))
             common.check_print_call(zip
                                     + [os.path.join(paths.result, args.name + '-signed.7z'),
-                                           app],
+                                       zippattern],
                                     signed_install_path)
 
 def get_paths(args):