Fix possible de-duping issues.

- Clean bad hashes from earlier release.
- Fix file equality comparison.
- Given our new de-duping, we don't want to run into a situation where two
simultaneous compressions could be happening on the same image.

src/org/thoughtcrime/securesms/database/helpers/SQLCipherOpenHelper.java

@@ -87,8 +87,9 @@ public class SQLCipherOpenHelper extends SQLiteOpenHelper {
   private static final int BLUR_HASH                        = 30;
   private static final int MMS_RECIPIENT_CLEANUP_2          = 31;
   private static final int ATTACHMENT_TRANSFORM_PROPERTIES  = 32;
+  private static final int ATTACHMENT_CLEAR_HASHES          = 33;
 
-  private static final int    DATABASE_VERSION = 32;
+  private static final int    DATABASE_VERSION = 33;
   private static final String DATABASE_NAME    = "signal.db";
 
   private final Context        context;
@@ -602,6 +603,10 @@ public class SQLCipherOpenHelper extends SQLiteOpenHelper {
         db.execSQL("ALTER TABLE part ADD COLUMN transform_properties TEXT DEFAULT NULL");
       }
 
+      if (oldVersion < ATTACHMENT_CLEAR_HASHES) {
+        db.execSQL("UPDATE part SET data_hash = null");
+      }
+
       db.setTransactionSuccessful();
     } finally {
       db.endTransaction();