Skip _oem_props if oem_dicts is None.

The oem_dicts in BuildInfo is only available to ota_from_target_files
when it's called with "--oem_settings" input. However, aosp/1135332
starts to use BuildInfo in add_img_to_target_files w/o oem_dicts. An
assert is triggered due to it when oem_fingerprint_properties is in the
info_dict.
This change skip _oem_props reading if oem_dicts is None to allow to
this case.

BUG: 155360923
BUG: 154171021
Test: Sign images with oem_fingerprint_properties.
Change-Id: I6a73feecd9567fd4d85f4eab3d4e11c5df28fe39

tools/releasetools/common.py

@@ -361,10 +361,13 @@ class BuildInfo(object):
     self.oem_dicts = oem_dicts
 
     self._is_ab = info_dict.get("ab_update") == "true"
-    self._oem_props = info_dict.get("oem_fingerprint_properties")
 
-    if self._oem_props:
-      assert oem_dicts, "OEM source required for this build"
+    # Skip _oem_props if oem_dicts is None to use BuildInfo in
+    # sign_target_files_apks
+    if self.oem_dicts:
+      self._oem_props = info_dict.get("oem_fingerprint_properties")
+    else:
+      self._oem_props = None
 
     def check_fingerprint(fingerprint):
       if (" " in fingerprint or any(ord(ch) > 127 for ch in fingerprint)):

tools/releasetools/test_common.py

@@ -176,10 +176,6 @@ class BuildInfoTest(test_utils.ReleaseToolsTestCase):
     self.assertEqual('brand3/product-name/device3:build-thumbprint',
                      target_info.fingerprint)
 
-    # Missing oem_dict should be rejected.
-    self.assertRaises(AssertionError, common.BuildInfo,
-                      self.TEST_INFO_DICT_USES_OEM_PROPS, None)
-
   def test_init_badFingerprint(self):
     info_dict = copy.deepcopy(self.TEST_INFO_DICT)
     info_dict['build.prop']['ro.build.fingerprint'] = 'bad fingerprint'