Fix for dropping projects when cancelling switch (#1780)

[jbalsas]

Possible fix for #1780

As @pthiess pointed out, checking to see if the folder exists to prevent it from being dropped.

[redmunds]

Please update this comment to something like:

// If folder does not exist on disk then remove the project from the list

[redmunds]

This looks good. Just a couple minor changes.

[jbalsas]

@redmunds It should be good to go now.

As a side note, passing fault codes in the reject calls could be helpful in cases like this. In this issue, there are at least 4 ways openProject can fail, and only one should require dropping the project from the list, but we need to check every time anyway.

A quick search reveals that less than half the reject calls are passing some error code, but I guess it can become a mess for some cases that end up chaining different promises though...

[redmunds]

This is not common case, so I think this is OK. Looks good. Merging.