Ignore malformed Xcode app bundles

[interstateone]

This changes Files.installed Xcodes to ignore app bundles that don't contain Info.plist files at the expected location instead of crashing. This change doesn't include a test to verify the new behaviour because the Entry type in the Path library doesn't have an accessible initializer, which is required to construct some test data without creating what I thought would be too many workarounds for testing's sake.

Manual test steps:

1. Create a directory in /Applications with a unique name like Xcode.app or Xcode-12.app.
2. make
3. .build/release/xcodes list should print the list of available and installed Xcodes and not crash

Closes #87

[csykes]

Hmmm... I still get the crash

chad@Chads-Mac ~/d/xcodes> mkdir /Applications/xcode-test.app
chad@Chads-Mac ~/d/xcodes> .build/release/xcodes list
Fatal error: 'try!' expression unexpectedly raised an error: Error Domain=NSCocoaErrorDomain Code=260 "The file “Info.plist” couldn’t be opened because there is no such file." UserInfo={NSFilePath=/Applications/xcode-test.app/Contents/Info.plist, NSUnderlyingError=0x7fb1026050f0 {Error Domain=NSPOSIXErrorDomain Code=2 "No such file or directory"}}: file /Users/chad/dev/xcodes/Sources/XcodesKit/Environment.swift, line 107
fish: '.build/release/xcodes list' terminated by signal SIGILL (Illegal instruction)

[csykes]

Ummm... on the master branch... is it just me or is this branch invisible on Github?

[interstateone]

Ummm... on the master branch... is it just me or is this branch invisible on Github?

It's from a fork, so it's not as straightforward to test as when it's in this remote.