gh-137396: Guard against negative offset in tarfile (GH-XXXXX)

Author: VbhvGupta

Lib/tarfile.py

@@ -1437,7 +1437,7 @@ def _proc_sparse(self, tarfile):
                     numbytes = nti(buf[pos + 12:pos + 24])
                 except ValueError:
                     break
-                if offset and numbytes:
+                if offset >= 0 and numbytes >= 0:
                     structs.append((offset, numbytes))
                 pos += 24
             isextended = bool(buf[504])