Ensure all commands fail early if patch file is not specified in options

[Dave Reid]

If drush_get_option('patch-file') is empty we should fail hard at the beginning of every command. Currently I don't think that is happening, or things are silently failing.

[Miloš Kroulík]

Yes, thats exactly what I'm experiencing. The output is like this:

[module] patched with [patchfile.patch].                                                                                                                                                                                        [success]
file_put_contents(): Filename cannot be empty patchfile.drush.inc:512                                                                                                                                                                          [warning]
Unable to append to file .                                                                                                                                                                                                                     [error]

[Honza Pobořil]

And it is important to give user understandable error message if variable is empty.

[Stanislav Popov]

Also would be good to check that patchfile exists. It allows to define patch-file in global config and affects only sites that has patchfile.