allow unpack msi if some cab are missing

--- a/src/LessMsi.Core/Msi/Wixtracts.cs
+++ b/src/LessMsi.Core/Msi/Wixtracts.cs
@@ -504,7 +504,7 @@ namespace LessMsi.Msi
 								Path originalCabFile = Path.Combine(msi.Parent, cabSourceName);
                                 if (!originalCabFile.Exists)
                                 {
-                                    throw ExternalCabNotFoundException.CreateFromCabPath(cabSourceName, msi.Parent.FullPathString);
+                                    continue; //throw ExternalCabNotFoundException.CreateFromCabPath(cabSourceName, msi.Parent.FullPathString);
                                 }
 								FileSystem.Copy(originalCabFile, localCabFile);
 							}