eslint-plugin-react-hooks version: 4.2.0

## Steps To Reproduce

I know it shouldn't exist in production code, but it's annoying while editing some files.

```js
import React, { useEffect } from "react";

const App = () => {
  useEffect(); // <-
  return null;
};

export default App;
```

Link to code example: https://codesandbox.io/s/polished-sun-3wr27?file=/src/App.js

## The current behavior

ESLint crashed.

```
TypeError: Cannot read property 'type' of undefined
```

## The expected behavior

ESLint doesn't crash but reports an error instead.
if (!Array.isArray(resolved.defs)) {
          return false;
        }
        const def = resolved.defs[0];
        if (def == null) {
          return false;
        }
        if (def.node == null || def.node.id == null) {
          return false;
        }
        
        
        const fnNode = def.node;
        const childScopes = componentScope.childScopes;
        let fnScope = null;
        let i;
        for (i = 0; i < childScopes.length; i++) {
          const childScope = childScopes[i];
          const childScopeBlock = childScope.block;
          if (
            
            (fnNode.type === 'FunctionDeclaration' &&
              childScopeBlock === fnNode) ||
            
            
            (fnNode.type === 'VariableDeclarator' &&
              childScopeBlock.parent === fnNode)
          ) {