Task times out when Theme file isn't found

[jessehouwing]

I switched from using a custom zip task to using yarn zip to build and zip my theme. The file name generated is slightly different. So slight that I hadn't noticed.

The task will happily try to upload a non-existent file and time-out. Then the screenshots will show this very interesting error message:

Took me a while to figure out what was wrong.

I suppose checking whether the file exists before trying to upload it would be the simplest solution.

Log:

2018-07-30T15:16:59.6263156Z ##[section]Starting: Ghost 
2018-07-30T15:16:59.6267235Z ==============================================================================
2018-07-30T15:16:59.6267540Z Task         : Ghost theme uploader
2018-07-30T15:16:59.6267786Z Description  : Upload a theme to a Ghost blog.
2018-07-30T15:16:59.6268031Z Version      : 1.0.1003
2018-07-30T15:16:59.6268244Z Author       : Geek Learning
2018-07-30T15:16:59.6268681Z Help         : [More Information](https://github.com/geeklearningio/gl-vsts-tasks-ghost/wiki/Ghost) (Version 1.0.1003).

Dear Angular and Ember CLI users, please check our [known issues](https://github.com/geeklearningio/gl-vsts-tasks-ghost/wiki/Known-Issues)
2018-07-30T15:16:59.6269181Z ==============================================================================
2018-07-30T15:17:00.0848237Z fb2da09f-1984-453f-8ec5-5269c96bc969 exists true
2018-07-30T15:17:01.1632731Z Opening blog:  https://scrumbug.ghost.io/
2018-07-30T15:17:08.9460360Z Logging in with   ***
2018-07-30T15:17:12.0541536Z Logged in with   ***
2018-07-30T15:17:12.2843812Z Navigating to the design section
2018-07-30T15:17:12.9166945Z Uploading theme:  D:\a\1\s\dist\jessehouwingnl-casper.zip
2018-07-30T15:19:13.4424855Z ##[error]Error: waiting for XPath "//h1[contains(.,'Upload successful!')]" failed: timeout 120000ms exceeded
2018-07-30T15:19:14.4079679Z ##[section]Async Command Start: Upload Artifact
2018-07-30T15:19:14.4080020Z Uploading 9 files
2018-07-30T15:19:15.2804564Z File upload succeed.
2018-07-30T15:19:15.2804944Z Upload 'D:\a\1\a\screenshots' to file container: '#/1415075/screenshots'
2018-07-30T15:19:15.2805594Z Associated artifact 970 with build 1644
2018-07-30T15:19:15.2805910Z ##[section]Async Command End: Upload Artifact
2018-07-30T15:19:15.2807322Z ##[section]Finishing: Ghost 

Actual file name:

D:\a\1\s\dist\casper-jessehouwingnl.zip