Fix AttributeError when progress_bar not initialized in UI mode

The installer crashes with 'AttributeError: Installer object has no
attribute progress_bar' when using kickstart with ui:true if an
exception occurs before the progress_bar is created.

Root cause:
- When ui:true in kickstart, install_config['ui'] is True
- execute() calls curses.wrapper(self._install)
- Inside _install(), progress_bar is created only AFTER curses init
- If exception occurs before progress_bar creation, exit_gracefully()
  is called which checks install_config['ui'] and tries to access
  progress_bar.hide() - this fails with AttributeError

Fix (surgical - only modifies exit_gracefully):
1. Initialize self.progress_bar = None in __init__()
2. Initialize self.window = None in __init__()
3. In exit_gracefully(), check 'progress_bar is not None' before hide()
4. In exit_gracefully(), check 'window is not None' before addstr()

This is a minimal fix that only affects error handling. Normal installer
flow is unchanged - progress_bar gets created in _install() before any
other code tries to use it.

Signed-off-by: Daniel Casota <daniel.casota@gmail.com>

Author: root

photon_installer/installer.py

@@ -133,6 +133,8 @@ def __init__(self, working_directory=Defaults.WORKING_DIRECTORY, rpm_path=None,
         self.ab_present = False
         self.mounts = []
         self.cwd = os.getcwd()
+        self.progress_bar = None  # Initialize to prevent AttributeError
+        self.window = None        # Initialize to prevent AttributeError
 
         # some keys can have arch specific variations
         for key in ['packages', 'linux_flavor']:
@@ -831,8 +833,9 @@ def exit_gracefully(self, signal1=None, frame1=None):
         del frame1
         if not self.exiting and self.install_config:
             self.exiting = True
-            if self.install_config['ui']:
+            if self.install_config['ui'] and self.progress_bar is not None:
                 self.progress_bar.hide()
+            if self.install_config['ui'] and self.window is not None:
                 self.window.addstr(0, 0, 'Oops, Installer got interrupted.\n\n' +
                                    'Press any key to get to the bash...')
                 self.window.content_window().getch()