Basic fix for pc_chd support in imgtool (#14148)

* imgtool: Take ownership of stream in pc_chd_image_open

`imgtool::image::internal_open` passes an rvalue reference to the stream to the `open` function of the image format module. It expects the `open` function to take ownership if it keeps a reference to the stream. If `open` does not do so, the `stream` is going to be destroyed at the end of `internal_open`.

`pc_chd_image_open` fails to take ownership, yet it persists a reference to the stream as part of `info->hard_disk`. This causes an use-after-free condition

* imgtool: Correct determination of total sectors of a FAT volume

The number of total sectors of a FAT volume is stored either in the 16-bit word at offset 19 or, if that word is zero, in the 32-bit word at offset 32 instead. The 32-bit word is not a high word to build a 48-bit value in conjunction with the 16-bit word at offset 19, but it supersedes it.

Author: karcherm

src/tools/imgtool/modules/fat.cpp

@@ -436,7 +436,7 @@ static imgtoolerr_t fat_partition_open(imgtool::partition &partition, uint64_t f
 	if (info->sectors_per_cluster == 0)
 		return IMGTOOLERR_CORRUPTIMAGE;
 
-	info->total_sectors = total_sectors_l + (uint64_t(total_sectors_h) << 16);
+	info->total_sectors = total_sectors_l != 0 ? total_sector_l : total_sectors_h;
 	available_sectors = info->total_sectors - info->reserved_sectors
 		- (info->sectors_per_fat * info->fat_count)
 		- (info->root_entries * FAT_DIRENT_SIZE + FAT_SECLEN - 1) / FAT_SECLEN;

src/tools/imgtool/modules/pc_hard.cpp

@@ -292,6 +292,7 @@ static imgtoolerr_t pc_chd_image_open(imgtool::image &image, imgtool::stream::pt
 	if (err)
 		return err;
 
+	stream.release();
 	return IMGTOOLERR_SUCCESS;
 }