fix: Fallback to xcodebuild vars for faulty Info.plist files

[kamilogorek]

This is sort of an edge-case, as XCode is not producing an Info.plist file
by default anymore. However, it still does so for some templates.

For example iOS Storyboard template will produce a partial Info.plist file,
with a content only related to the Storyboard itself, but not the project as a whole. eg.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>UIApplicationSceneManifest</key>
    <dict>
        <key>UISceneConfigurations</key>
        <dict>
            <key>UIWindowSceneSessionRoleApplication</key>
            <array>
                <dict>
                    <key>UISceneStoryboardFile</key>
                    <string>Main</string>
                </dict>
            </array>
        </dict>
    </dict>
</dict>
</plist>

This causes a false-positive in this branch, as INFOPLIST_FILE is present, yet it contains
no data required by the CLI to correctly produce a InfoPlist struct.

In the case like that, we try to fallback to variables produced by xcodebuild binary,
and read them directly, just like we do in from_xcode_env method.

Fixes #1301