fix header/footer item ID issue

fixes #4667
Closes #4685
// FREEBIE

src/org/thoughtcrime/securesms/contacts/ContactSelectionListAdapter.java

@@ -178,17 +178,6 @@ public class ContactSelectionListAdapter extends CursorRecyclerViewAdapter<ViewH
     return cursor.getInt(cursor.getColumnIndexOrThrow(ContactsDatabase.CONTACT_TYPE_COLUMN)) == ContactsDatabase.PUSH_TYPE;
   }
 
-  private Cursor getCursorAtPositionOrThrow(int position) {
-    Cursor cursor = getCursor();
-    if (cursor == null) {
-      throw new IllegalStateException("Cursor should not be null here.");
-    }
-    if (!cursor.moveToPosition(position)) {
-      throw new IllegalStateException("Cursor couldn't be moved to position.");
-    }
-    return cursor;
-  }
-
   public interface ItemClickListener {
     void onItemClick(ContactSelectionListItem item);
   }

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

@@ -35,8 +35,10 @@ public abstract class CursorRecyclerViewAdapter<VH extends RecyclerView.ViewHold
   private final Context context;
   private final DataSetObserver observer = new AdapterDataSetObserver();
 
-  @VisibleForTesting final static int HEADER_TYPE = Integer.MIN_VALUE;
-  @VisibleForTesting final static int FOOTER_TYPE = Integer.MIN_VALUE + 1;
+  @VisibleForTesting static final int  HEADER_TYPE = Integer.MIN_VALUE;
+  @VisibleForTesting static final int  FOOTER_TYPE = Integer.MIN_VALUE + 1;
+  @VisibleForTesting static final long HEADER_ID   = Long.MIN_VALUE;
+  @VisibleForTesting static final long FOOTER_ID   = Long.MIN_VALUE + 1;
 
   private           Cursor  cursor;
   private           boolean valid;
@@ -143,8 +145,7 @@ public abstract class CursorRecyclerViewAdapter<VH extends RecyclerView.ViewHold
   @Override
   public final void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
     if (!isHeaderPosition(position) && !isFooterPosition(position)) {
-      moveToPositionOrThrow(getCursorPosition(position));
-      onBindItemViewHolder((VH)viewHolder, cursor);
+      onBindItemViewHolder((VH)viewHolder, getCursorAtPositionOrThrow(position));
     }
   }
 
@@ -154,8 +155,7 @@ public abstract class CursorRecyclerViewAdapter<VH extends RecyclerView.ViewHold
   public final int getItemViewType(int position) {
     if (isHeaderPosition(position)) return HEADER_TYPE;
     if (isFooterPosition(position)) return FOOTER_TYPE;
-    moveToPositionOrThrow(getCursorPosition(position));
-    return getItemViewType(cursor);
+    return getItemViewType(getCursorAtPositionOrThrow(position));
   }
 
   public int getItemViewType(@NonNull Cursor cursor) {
@@ -164,25 +164,24 @@ public abstract class CursorRecyclerViewAdapter<VH extends RecyclerView.ViewHold
 
   @Override
   public final long getItemId(int position) {
-    moveToPositionOrThrow(getCursorPosition(position));
-    return getItemId(cursor);
+    if (isHeaderPosition(position)) return HEADER_ID;
+    if (isFooterPosition(position)) return FOOTER_ID;
+    long itemId = getItemId(getCursorAtPositionOrThrow(position));
+    return itemId <= Long.MIN_VALUE + 1 ? itemId + 2 : itemId;
   }
 
   public long getItemId(@NonNull Cursor cursor) {
     return cursor.getLong(cursor.getColumnIndexOrThrow("_id"));
   }
 
-  private void assertActiveCursor() {
+  protected @NonNull Cursor getCursorAtPositionOrThrow(final int position) {
     if (!isActiveCursor()) {
       throw new IllegalStateException("this should only be called when the cursor is valid");
     }
-  }
-
-  private void moveToPositionOrThrow(final int position) {
-    assertActiveCursor();
-    if (!cursor.moveToPosition(position)) {
+    if (!cursor.moveToPosition(getCursorPosition(position))) {
       throw new IllegalStateException("couldn't move cursor to position " + position);
     }
+    return cursor;
   }
 
   private boolean isActiveCursor() {