fix(ios): guard against nil localizedDescription in didFailToLocateUserWithError

[isaacrowntree]

Summary

Fixes a crash in AIRMapManager.m where error.localizedDescription can be nil, causing an NSInvalidArgumentException when constructing the NSDictionary literal.

Crash:

NSInvalidArgumentException: *** -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: 
attempt to insert nil object from objects[0]

Stack trace:

-[AIRMapManager mapView:didFailToLocateUserWithError:] (AIRMapManager.m:1244)
-[MKMapView locationManagerFailedToUpdateLocation:withError:]
-[MKLocationManager _reportLocationFailureWithError:]

Root cause

NSError.localizedDescription is documented to always return a non-nil string, but edge cases exist (custom error domains, specific iOS versions) where it can return nil. The Objective-C dictionary literal @{ @"message": nil } crashes immediately.

Fix

Add a nil-coalescing fallback: error.localizedDescription ?: @"Unknown error"

This is a one-line change with zero risk — it only affects the nil case which currently crashes.

Related

• Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[0]' #5505 — same crash signature, closed without code fix
• initWithObjects:forKeys:count:]: attempt to insert nil object from objects[2]' #5528 — similar nil object crash pattern
• fix(ios): add nil check for subview insertion in Apple Maps #5871 — related nil check PR for a different method

Test plan

• Verified the fix compiles in Xcode
• Confirmed the crash no longer occurs when localizedDescription is nil
• No behavioral change for the normal (non-nil) case