Fix use-after-free race in RCTInstance callFunctionOnJSModule (#58816)

Summary:
WARNING: Generated by Autopilot (alpha) — review carefully, verify the underlying claim before accepting.
Agent: Bugs Agent | Trajectory: https://www.internalfb.com/intern/devai/devmate/inspector/625bbaa5-e1a4-4e06-9838-cc789cf43c8f/ | SC job: https://www.internalfb.com/intern/sandcastle/instance/9007202252272448/

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## Changelog:

[Internal]

Reviewed By: zeyap

Differential Revision: D122831570

Author: Autopilot Bot

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTInstance.mm

@@ -171,10 +171,14 @@ - (void)dealloc
 
 - (void)callFunctionOnJSModule:(NSString *)moduleName method:(NSString *)method args:(NSArray *)args
 {
-  if (_valid) {
-    _reactInstance->callFunctionOnModule(
-        [moduleName UTF8String], [method UTF8String], convertIdToFollyDynamic(args ? args : @[]));
+  // This is called from arbitrary threads, while -invalidate destroys _reactInstance on
+  // the JS thread, so checking _valid and dereferencing have to happen as one step.
+  std::lock_guard<std::mutex> lock(_invalidationMutex);
+  if (!_valid || !_reactInstance) {
+    return;
   }
+  _reactInstance->callFunctionOnModule(
+      [moduleName UTF8String] ?: "", [method UTF8String] ?: "", convertIdToFollyDynamic(args ? args : @[]));
 }
 
 - (void)invalidate