Add null check when loading data from manifest

[fractalwrench]

Goal

Adds a null check when loading meta-data from the manifest. In a React Native 0.55 example app with no meta-data elements present in the manifest, applicationInfo.metadata was returned as null by the PackageManager.

It's hypothesised that this was caused by a very old targetSdkVersion/compileSdkVersion, and can be demonstrated to be caused by the lack of any meta-data elements in the manifest, making this a relatively rare scenario. A null check has been added regardless.

[bugsnagbot]

Android notifier sizes

Format	Size impact of Bugsnag (kB)	Size impact of Bugsnag when Minified (kB)
APK	1434.34	1363.74
arm64_v8a	365.78	293.15
armeabi	344.28	271.64
armeabi_v7a	327.08	254.44
x86	403.77	331.13
x86_64	386.45	313.81

Generated by 🚫 Danger

[bengourley]

Confirmed, this is now working on the project where the issue was identified.