fix: safe check for config command

[stephenlacy]

Summary:

Fixes issues building for android when react-native.config.js has packages with platforms filter

Test Plan:

With the latest version of cli create/modify the react-native.config.js with a package and any platform as such:

module.exports = {
  dependencies: {
    'interactable': {
      platforms: {
        ios: null, 
      },
    },
    'appcenter': {
      platforms: {
        android: null,
      },
    },
  }
}

The cli will build without throwing the error TypeError: Cannot convert undefined or null to object at Function.keys () at isValidRNDependency

[thymikee]

Thanks!