Handle quote position task finishing after fragment detaches.

There's a chance that the AsyncTask that retrieves a quoted message's
position could finish after the fragment is detached, which would cause
a crash. I've changed it so if this case occurs, the result is ignored.

Also, I noticed that when searching the message table, if a quote can't
be found, we'd end up traversing the entire table. To prevent this from
taking forever on large message tables, I've limited it to searchin only
what is currently present in the adapter.

Fixes #7756

src/org/thoughtcrime/securesms/ConversationFragment.java

@@ -620,12 +620,24 @@ public class ConversationFragment extends Fragment
       new AsyncTask<Void, Void, Integer>() {
         @Override
         protected Integer doInBackground(Void... voids) {
+          if (getActivity() == null || getActivity().isFinishing()) {
+            Log.w(TAG, "Task to retrieve quote position started after the fragment was detached.");
+            return 0;
+          }
           return DatabaseFactory.getMmsSmsDatabase(getContext())
-                                .getQuotedMessagePosition(threadId, messageRecord.getQuote().getId(), messageRecord.getQuote().getAuthor());
+                                .getQuotedMessagePosition(threadId,
+                                                          messageRecord.getQuote().getId(),
+                                                          messageRecord.getQuote().getAuthor(),
+                                                          getListAdapter().getItemCount());
         }
 
         @Override
         protected void onPostExecute(Integer position) {
+          if (getActivity() == null || getActivity().isFinishing()) {
+            Log.w(TAG, "Task to retrieve quote position finished after the fragment was detached.");
+            return;
+          }
+
           if (position >= 0 && position < getListAdapter().getItemCount()) {
             list.scrollToPosition(position);
             getListAdapter().pulseHighlightItem(position);

src/org/thoughtcrime/securesms/database/MmsSmsDatabase.java

@@ -158,11 +158,11 @@ public class MmsSmsDatabase extends Database {
     DatabaseFactory.getMmsDatabase(context).incrementReceiptCount(syncMessageId, timestamp, false, true);
   }
 
-  public int getQuotedMessagePosition(long threadId, long quoteId, @NonNull Address address) {
+  public int getQuotedMessagePosition(long threadId, long quoteId, @NonNull Address address, int limit) {
     String order     = MmsSmsColumns.NORMALIZED_DATE_RECEIVED + " DESC";
     String selection = MmsSmsColumns.THREAD_ID + " = " + threadId;
 
-    try (Cursor cursor = queryTables(new String[]{ MmsSmsColumns.NORMALIZED_DATE_SENT, MmsSmsColumns.ADDRESS }, selection, order, null)) {
+    try (Cursor cursor = queryTables(new String[]{ MmsSmsColumns.NORMALIZED_DATE_SENT, MmsSmsColumns.ADDRESS }, selection, order, String.valueOf(limit))) {
       String  serializedAddress = address.serialize();
       boolean isOwnNumber       = Util.isOwnNumber(context, address);