archive/iso9660: implement seeking

NEWS

@@ -6,6 +6,7 @@ ver 0.21.26 (not yet released)
   - bzip2: fix crash on corrupt bzip2 file
   - bzip2: flush output at end of input file
   - iso9660: fix unaligned reads
+  - iso9660: support seeking
   - zzip: fix crash on corrupt ZIP file
 * decoder
   - sndfile: fix lost samples at end of file

src/archive/plugins/Iso9660ArchivePlugin.cxx

@@ -198,12 +198,20 @@ public:
 		 lsn(_lsn)
 	{
 		size = _size;
+		seekable = true;
 		SetReady();
 	}
 
 	/* virtual methods from InputStream */
 	bool IsEOF() noexcept override;
 	size_t Read(void *ptr, size_t size) override;
+
+	void Seek(offset_type new_offset) override {
+		if (new_offset > size)
+			throw std::runtime_error("Invalid seek offset");
+
+		offset = new_offset;
+	}
 };
 
 InputStreamPtr