pw_doctor: Improve deleted file error message

Previously the user just got an exception.

Change-Id: Iad2271640e650b7a21b234f8908b5eebd9343083
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/97740
Reviewed-by: Jonathan Cardy <jonathancardy@google.com>
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/pw_doctor/py/pw_doctor/doctor.py b/pw_doctor/py/pw_doctor/doctor.py
index d3a735c..fea164d 100755
--- a/pw_doctor/py/pw_doctor/doctor.py
+++ b/pw_doctor/py/pw_doctor/doctor.py
@@ -377,6 +377,12 @@
 
     for json_path in json_paths:
         ctx.debug(f'Checking packages in {json_path}')
+        if not json_path.exists():
+            ctx.error(
+                'CIPD package file %s may have been deleted, please '
+                'rerun bootstrap', json_path)
+            continue
+
         install_path = pathlib.Path(
             cipd_update.package_installation_path(cipd_dir, json_path))
         for package in json.loads(json_path.read_text()).get('packages', ()):