Fix getting unix modification time in ZIP files

InfoZIP actually does respect a file's modification time, even if the access time and/or creation time are not set.

Author: bastianeicher

src/ICSharpCode.SharpZipLib/Zip/ZipEntry.cs

@@ -1103,12 +1103,7 @@ private DateTime GetDateTime(ZipExtraData extraData)
 
 			// Check for Unix timestamp
 			ExtendedUnixData unixData = extraData.GetData<ExtendedUnixData>();
-			if (unixData != null &&
-				// Only apply modification time, but require all other values to be present
-				// This is done to match InfoZIP's behaviour
-				((unixData.Include & ExtendedUnixData.Flags.ModificationTime) != 0) &&
-				((unixData.Include & ExtendedUnixData.Flags.AccessTime) != 0) &&
-				((unixData.Include & ExtendedUnixData.Flags.CreateTime) != 0))
+			if (unixData != null && unixData.Include.HasFlag(ExtendedUnixData.Flags.ModificationTime))
 				return unixData.ModificationTime;
 
 			// Fall back to DOS time