Add a missing default value for OPTIONS.extracted_input.

Test: ota_from_target_files.py without --extracted_input_target_files.
Change-Id: Ieaba43fa557b544b24f3eeccd68ac289d1fe3d31

Author: Tao Bao

tools/releasetools/ota_from_target_files.py

@@ -180,6 +180,7 @@
 OPTIONS.log_diff = None
 OPTIONS.payload_signer = None
 OPTIONS.payload_signer_args = []
+OPTIONS.extracted_input = None
 
 METADATA_NAME = 'META-INF/com/android/metadata'
 UNZIP_PATTERN = ['IMAGES/*', 'META/*']