fix: non-null check before calling nativeModule in OCR controllers (#755)

## Description

<!-- Provide a concise and descriptive summary of the changes
implemented in this PR. -->

### Introduces a breaking change?

- [ ] Yes
- [x] No

### Type of change

- [x] Bug fix (change which fixes an issue)
- [ ] New feature (change which adds functionality)
- [ ] Documentation update (improves or adds clarity to existing
documentation)
- [ ] Other (chores, tests, code style improvements etc.)

### Tested on

- [ ] iOS
- [ ] Android

### Testing instructions

<!-- Provide step-by-step instructions on how to test your changes.
Include setup details if necessary. -->

### Screenshots

<!-- Add screenshots here, if applicable -->

### Related issues

<!-- Link related issues here using #issue-number -->

### Checklist

- [ ] I have performed a self-review of my code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have updated the documentation accordingly
- [ ] My changes generate no new warnings

### Additional notes

<!-- Include any additional information, assumptions, or context that
reviewers might need to understand this PR. -->

Author: chmjkb

packages/react-native-executorch/src/controllers/LLMController.ts

@@ -215,7 +215,9 @@ export class LLMController {
       );
     }
     this.onToken = () => {};
-    this.nativeModule.unload();
+    if (this.nativeModule) {
+      this.nativeModule.unload();
+    }
     this.isReadyCallback(false);
     this.isGeneratingCallback(false);
   }
@@ -245,10 +247,22 @@ export class LLMController {
   }
 
   public interrupt() {
+    if (!this.nativeModule) {
+      throw new RnExecutorchError(
+        RnExecutorchErrorCode.ModuleNotLoaded,
+        "Cannot interrupt a model that's not loaded."
+      );
+    }
     this.nativeModule.interrupt();
   }
 
   public getGeneratedTokenCount(): number {
+    if (!this.nativeModule) {
+      throw new RnExecutorchError(
+        RnExecutorchErrorCode.ModuleNotLoaded,
+        "Cannot get token count for a model that's not loaded."
+      );
+    }
     return this.nativeModule.getGeneratedTokenCount();
   }
 

packages/react-native-executorch/src/controllers/OCRController.ts

@@ -103,7 +103,9 @@ export class OCRController {
         'The model is currently generating. Please wait until previous model run is complete.'
       );
     }
-    this.nativeModule.unload();
+    if (this.nativeModule) {
+      this.nativeModule.unload();
+    }
     this.isReadyCallback(false);
     this.isGeneratingCallback(false);
   }

packages/react-native-executorch/src/controllers/VerticalOCRController.ts

@@ -106,7 +106,9 @@ export class VerticalOCRController {
         'The model is currently generating. Please wait until previous model run is complete.'
       );
     }
-    this.ocrNativeModule.unload();
+    if (this.ocrNativeModule) {
+      this.ocrNativeModule.unload();
+    }
     this.isReadyCallback(false);
     this.isGeneratingCallback(false);
   }

packages/react-native-executorch/src/hooks/natural_language_processing/useLLM.ts

@@ -68,7 +68,9 @@ export const useLLM = ({
     })();
 
     return () => {
-      controllerInstance.delete();
+      if (controllerInstance.isReady) {
+        controllerInstance.delete();
+      }
     };
   }, [
     controllerInstance,