Fix bug in APK entry alignment.

APK entry alignment logic assumes that input entries have zero-length
comment and extra fields. When the assumption is broken, the logic
silently breaks alignment of output entries. This happens, for
example, when the APK to be signed is already aligned and thus may
contain entries with non-empty extra fields.

Given that APKs are not supposed to use comment and extra fields for
anything useful and given that this signer already discards comment
and extra fields of compressed entries, this change makes the signer
discard comment and extra fields of STORED input entries as well.
This unbreaks the existing alignment logic.

Bug: 27814973

(cherry picked from commit 37a0ecd329)

Change-Id: If2e0df6d3298e9736ef175bb0d9a05d450164c9f

tools/signapk/src/com/android/signapk/SignApk.java

@@ -544,6 +544,11 @@ class SignApk {
             // Preserve the STORED method of the input entry.
             outEntry = new JarEntry(inEntry);
             outEntry.setTime(timestamp);
+            // Discard comment and extra fields of this entry to
+            // simplify alignment logic below and for consistency with
+            // how compressed entries are handled later.
+            outEntry.setComment(null);
+            outEntry.setExtra(null);
 
             // 'offset' is the offset into the file at which we expect
             // the file data to begin.  This is the value we need to