Fix rc5 audit findings: exact libfreemkv pin, cdb test coverage

- ld/Cargo.toml: pin libfreemkv = "=1.0.0-rc.4.3" (exact, fail-closed)
  instead of the bare caret that accepted later 1.0.0 prereleases.
- ld/src/cdb.rs: replace the duplicate (2,0x44) assertion with a real
  wrong-mode/right-buffer case (0,0x77) so the 'Wrong mode, right buffer
  id' comment is actually exercised.

ld/Cargo.toml

@@ -8,7 +8,7 @@ description = "LibreDrive unlocker plugin for libfreemkv (firmware unlock for Me
 repository = "https://github.com/freemkv/freemkv-unlock"
 
 [dependencies]
-libfreemkv = "1.0.0-rc.4.3"
+libfreemkv = "=1.0.0-rc.4.3"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 base64 = "0.22.1"

ld/src/cdb.rs

@@ -47,7 +47,7 @@ mod tests {
         assert!(!is_unlock_read_buffer(1, 0x77));
         assert!(!is_unlock_read_buffer(2, 0x44));
         // Wrong mode, right buffer id.
-        assert!(!is_unlock_read_buffer(2, 0x44));
+        assert!(!is_unlock_read_buffer(0, 0x77));
         assert!(!is_unlock_read_buffer(0, 0x44));
         assert!(!is_unlock_read_buffer(3, 0x77));
         // Ordinary data reads.