Fix remaining compiler warnings: sign conversion and format string

- digest.c: Cast to ssize_t instead of size_t when assigning negative values to bytes_skip_following_chunks
- appimagetool_sign.c: Use %lld format specifier with (long long) cast for off_t type

These fixes address all remaining -Werror warnings on all architectures.

Co-authored-by: probonopd <[email protected]>

Author: Copilot

src/appimagetool_sign.c

@@ -213,7 +213,7 @@ bool embed_data_in_elf_section(const char* filename, const char* elf_section, gp
     }
 
     if (verbose) {
-        fprintf(stderr, "[sign] data size: %lu\n", data_size);
+        fprintf(stderr, "[sign] data size: %lld\n", (long long)data_size);
     }
 
     // rewind so we can later read the data

src/digest.c

@@ -68,7 +68,7 @@ bool appimage_type2_digest_md5(const char* path, char* digest) {
             // if bytes_left is now < 0, the section exceeds the current chunk
             // this amount of bytes needs to be skipped in the future sections
             if (bytes_left_this_chunk < 0) {
-                bytes_skip_following_chunks = (size_t) (-1 * bytes_left_this_chunk);
+                bytes_skip_following_chunks = (ssize_t) (-1 * bytes_left_this_chunk);
                 bytes_left_this_chunk = 0;
             }
 
@@ -88,7 +88,7 @@ bool appimage_type2_digest_md5(const char* path, char* digest) {
             // if bytes_left is now < 0, the section exceeds the current chunk
             // this amount of bytes needs to be skipped in the future sections
             if (bytes_left_this_chunk < 0) {
-                bytes_skip_following_chunks = (size_t) (-1 * bytes_left_this_chunk);
+                bytes_skip_following_chunks = (ssize_t) (-1 * bytes_left_this_chunk);
                 bytes_left_this_chunk = 0;
             }
 
@@ -108,7 +108,7 @@ bool appimage_type2_digest_md5(const char* path, char* digest) {
             // if bytes_left is now < 0, the section exceeds the current chunk
             // this amount of bytes needs to be skipped in the future sections
             if (bytes_left_this_chunk < 0) {
-                bytes_skip_following_chunks = (size_t) (-1 * bytes_left_this_chunk);
+                bytes_skip_following_chunks = (ssize_t) (-1 * bytes_left_this_chunk);
                 bytes_left_this_chunk = 0;
             }