Fix paths with spaces in $APPLE_PLUGIN_LIBRARY_ROOT for Apple.Core

[Lartu]

When trying to build our Unity project in a particular path that had spaces in it, we encountered this error:

No Apple plug-in library path found at /Users/Lartu/No Sync/[redacted] Build/ApplePluginLibraries
Please check the Unity Editor build output and/or logs for issues and errors.
Command PhaseScriptExecution failed with a nonzero exit code

This prevented us from building and Googling this issue yielded no fixes. In the end, it turns out that the build script for the Embed Apple Plug-in Libraries Build Phase does not enclose the $APPLE_PLUGIN_LIBRARY_ROOT variable with double quotes in the first conditional that checks for the existence of the library directory. This results in paths with spaces becoming multiple arguments for the [ command of the if line, which crashes the build process:

I've thus enclosed the variable with double quotes so this script works with paths that have spaces in them.

[Lartu]

I've just seen that this is fixed in another PR (#31), although the other solution is not POSIX compliant, and doesn't follow the same quoting format used in the rest of the script.

[Lartu]

In case anybody else comes across this issue (iPhone.build/Script-6BB2407B836CA087446EFB5.sh: line 13: [: too many arguments) before it's merged and fixed, to get your project to build you have to:

1. In Xcode go to the Unity-iPhone build target.
2. Once there, go to the Build Phases tab.
3. Scroll down to Embed Apple Plug-in Libraries and add these quotes to the script:

[VMaldecoasago]

@Lartu the script is already not POSIX compliant, since line 12 also uses the double squared-brackets. Also, #44 does some essential extra fixes. Can you please close this one, so that it's easier for Apple to decide which one to merge?

[Lartu]

@VMaldecoasago Amazing! Closing in favour of #44. Thank you!