Make 'image_offset' unsigned

Since 'image_offset' represents a file offset, it is always unsigned. Make
its type unsigned to prevent that a cast has to be introduced in the next
patch when assigning an image offset to the 'lo_offset' member.

Bug: 194450129
Test: Built Android images and installed these on an Android phone.
Change-Id: I884d91647669560148c5f62cef68633b1a8c7a7d
Signed-off-by: Bart Van Assche <bvanassche@google.com>

apexd/apex_file.cpp

diff --git a/apexd/apex_file.cpp b/apexd/apex_file.cpp
index 152e580..91be4a2 100644
--- a/apexd/apex_file.cpp
+++ b/apexd/apex_file.cpp
@@ -62,7 +62,7 @@
 constexpr const FsMagic kFsType[] = {{"f2fs", 1024, 4, "\x10\x20\xf5\xf2"},
                                      {"ext4", 1024 + 0x38, 2, "\123\357"}};
 
-Result<std::string> RetrieveFsType(borrowed_fd fd, int32_t image_offset) {
+Result<std::string> RetrieveFsType(borrowed_fd fd, uint32_t image_offset) {
   for (const auto& fs : kFsType) {
     char buf[fs.len];
     if (!ReadFullyAtOffset(fd, buf, fs.len, image_offset + fs.offset)) {
@@ -78,7 +78,7 @@
 }  // namespace
 
 Result<ApexFile> ApexFile::Open(const std::string& path) {
-  std::optional<int32_t> image_offset;
+  std::optional<uint32_t> image_offset;
   std::optional<size_t> image_size;
   std::string manifest_content;
   std::string pubkey;