Add nil checks to +[RCTInspectorDevServerHelper connectWithBundleURL:]

[amgleitman]

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native-macos 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native-macos 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

Summary

We saw a downstream ASan crash in +[RCTInspectorDevServerHelper connectWithBundleURL:].

It's not clear exactly what's causing the crash, but the stack trace includes a reference to -[__NSDictionaryM setObject:forKeyedSubscript:] along with the message "Hint: address points to the zero page." Since NSDictionary is known to misbehave when we try passing in nil as a key or value, one easy fix we can do is to add some nil checks and bail out in case we're about to do something sketchy.

Changelog

[Internal] [Fix] - bug fixes