Only enable zucchini if configuration file exists

Only enable zucchini if configuration file zucchini_config.txt exits
in target files and version in source and target is the same.

Without this patch zucchini would be enabled if configuration file
was missing from both target files.

Bug: 231204699
Test: Run ota package generation with zucchini_config.txt missing from
      both source and target zips. Confirm that zucchini is disabled.
Change-Id: Ia34998fd911d5860b38fe49fa5a88056a22d661e

tools/releasetools/ota_from_target_files.py

@@ -1208,6 +1208,8 @@ def GenerateAbOtaPackage(target_file, output_file, source_file=None):
         metadata.postcondition.partition_state)
 
   if not ota_utils.IsZucchiniCompatible(source_file, target_file):
+    logger.warning(
+        "Builds doesn't support zucchini, or source/target don't have compatible zucchini versions. Disabling zucchini.")
     OPTIONS.enable_zucchini = False
 
   additional_args += ["--enable_zucchini",

tools/releasetools/ota_utils.py

@@ -693,6 +693,7 @@ def IsZucchiniCompatible(source_file: str, target_file: str):
       if os.path.exists(entry_path):
         with open(entry_path, "r") as fp:
           return fp.read()
-      else:
-        return ""
-  return ReadEntry(source_file, _ZUCCHINI_CONFIG_ENTRY_NAME) == ReadEntry(target_file, _ZUCCHINI_CONFIG_ENTRY_NAME)
+    return False
+  sourceEntry = ReadEntry(source_file, _ZUCCHINI_CONFIG_ENTRY_NAME)
+  targetEntry = ReadEntry(target_file, _ZUCCHINI_CONFIG_ENTRY_NAME)
+  return sourceEntry and targetEntry and sourceEntry == targetEntry