Add nil check to RCTBaseInputTextView

[lyzhan7]

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

Currently seeing a crash in RCTBaseInputTextView when attempting to change formatting via the touch bar (ex. changing colors). The crash is occurring somewhere in the textInputShouldChangeText method. Here is the crash stack:

Crashed thread: 0
uncaught ObjC exception, reason: *** -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[0]

Last Exception Backtrace:
0   CoreFoundation                      0x0000000183ff0650 __exceptionPreprocess + 176
1   merp                                0x000000010a87d49c MerpPreprocessObjCException + 44
2   libobjc.A.dylib                     0x0000000183ae9eb4 objc_exception_throw + 60
3   CoreFoundation                      0x0000000183f07f94 -[__NSPlaceholderDictionary initWithObjects:forKeys:count:] + 728
4   CoreFoundation                      0x0000000183f07c90 +[NSDictionary dictionaryWithObjects:forKeys:count:] + 52
5   .......                             0x000000011bbbf1a8 -[RCTBaseTextInputView textInputShouldChangeText:inRange:] + 920

The crash looks like it's happening when we're creating a dictionary, and as far as I can tell this is the only dictionary being created in this method. The error message is specifically complaining about the first entry into the dictionary being nil, so I added a nil check here.

Changelog

Test Plan

The crash is only repro'ing in ship builds, and not debug builds, so will validate whether this change fixes the issue once the change makes it into the right build.

[Saadnajmi]

Also backport to 0.71-stable plz :)