Rebuild recovery-from-boot patch when calling add_img_to_target_files.

When using Verified Boot 2.0, releasetools specifies a salt value based
on build fingerprint, so that to give idempotent images.

However, the change that removed static `ro.build.fingerprint` [1] broke
the behavior, as common.LoadInfoDict still relies on fingerprints.
Without a fixed salt, the first call to make_recovery_patch.py and the
second one (which writes IMAGES/{boot,recovery}.img) will see different
images, which leads to install-recovery.sh failure.

Note that currently there's a dependency that requires getting bootable
images through two separate calls. make_recovery_patch.py has to happen
first to get (placeholder) files in the system image. We then generate
canned fs_config files, and finally use add_img_to_target_files.py to
write the images.

This CL adds a quick workaround to force rebuilding the
recovery-from-boot patch while calling add_img_to_target_files.py.

[1] https://android-review.googlesource.com/c/platform/build/+/892933

Bug: 134123803
Bug: 134525174
Test: TreeHugger
Test: Build a non-A/B target that uses AVB. Run validate_target_files.py
      on the generated target_files.zip.
Change-Id: I5859e30be63bfd54398cf41fd2d907f15285f560
diff --git a/tools/releasetools/add_img_to_target_files.py b/tools/releasetools/add_img_to_target_files.py
index 4156c8b..ebaa867 100755
--- a/tools/releasetools/add_img_to_target_files.py
+++ b/tools/releasetools/add_img_to_target_files.py
@@ -28,7 +28,8 @@
 
   -r  (--rebuild_recovery)
       Rebuild the recovery patch and write it to the system image. Only
-      meaningful when system image needs to be rebuilt.
+      meaningful when system image needs to be rebuilt and there're separate
+      boot / recovery images.
 
   --replace_verity_private_key
       Replace the private key used for verity signing. (same as the option
@@ -164,7 +165,8 @@
       else:
         common.ZipWrite(output_zip, ofile.name, arc_name)
 
-  if OPTIONS.rebuild_recovery:
+  if (OPTIONS.rebuild_recovery and recovery_img is not None and
+      boot_img is not None):
     logger.info("Building new recovery patch")
     common.MakeRecoveryPatch(OPTIONS.input_tmp, output_sink, recovery_img,
                              boot_img, info_dict=OPTIONS.info_dict)