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 skips _oem_props reading if oem_dicts is None to allow this
case.

BUG: 155360923
BUG: 154171021
Test: Sign images with oem_fingerprint_properties.
Change-Id: I6a73feecd9567fd4d85f4eab3d4e11c5df28fe39
Merged-In: Idfd41c8b20b23d50e4895f24500f9a25625b7d98

tools/releasetools/common.py

@@ -360,10 +360,13 @@ 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)):