file_iterator: always map at least one block.

Desired size of 0 would result in a noop for uncompressed blocks,
resulting in inconsistend behavior depending whether the block is
compressed, which ignores the desired size, or uncompressed, which
honors the desired size.

lib/file/file_iterator.c

@@ -141,13 +141,6 @@ map_block_uncompressed(
 	uint64_t outer_size = 0;
 	const size_t remaining_direct = sqsh__map_reader_remaining_direct(reader);
 
-	// Always try do map at least one block. This is needed for consistent
-	// behavior between implementations that ignore desired_size and
-	// implementations that honor it.
-	if (desired_size == 0) {
-		desired_size = 1;
-	}
-
 	for (; iterator->sparse_size == 0 && block_index < block_count;
 		 block_index++) {
 		if (sqsh_file_block_is_compressed(file, block_index)) {
@@ -280,6 +273,14 @@ sqsh_file_iterator_next(
 
 	sqsh__extract_view_cleanup(&iterator->extract_view);
 
+	// Desired size of 0 would result in a noop for uncompressed blocks,
+	// resulting in inconsistend behavior depending whether the block is
+	// compressed, which ignores the desired size, or uncompressed, which
+	// honors the desired size.
+	if (desired_size == 0) {
+		desired_size = 1;
+	}
+
 	if (iterator->sparse_size > 0) {
 		return map_zero_block(iterator);
 	} else if (iterator->block_index < block_count) {