[TAR] Add fileprivate extension to Data which works like String.padding and Data.prefix combined

Sources/TAR/TarEntryInfo.swift

@@ -255,3 +255,15 @@ public struct TarEntryInfo: ContainerEntryInfo {
     }
 
 }
+
+fileprivate extension Data {
+
+    /// This works (hopefully) in the same way as `String.padding(toLength: length, withPad: "\0", startingAt: 0)`.
+    @inline(__always)
+    private func zeroPad(_ length: Int) -> Data {
+        var out = length < self.count ? self.prefix(upTo: length) : self
+        out.append(Data(count: length - out.count))
+        return out
+    }
+
+}