when function write inside if condition statment, the declare function will only usable in that statment

**Describe the bug**
when function write inside if condition statment, the declare function will only usable in that statment

**To Reproduce**
I wrote example program, and upload to my github repo, please check this href https://github.com/LaiHuanMin/babelminify-issuecheck-for-function-scope

origin js
```
window.onload = () => {
var obj = {
testfunc: function(value){
if(value === 'test1'){
function scopefunc1(){
console.log('this is scope func 1');
}
var scopefunc2 = () => {
console.log();
console.log('this is scope func 2');
}
let scopefunc3 = () => {

}
}
// that func should be exists
scopefunc1();
// if the if condition is true, also should be exists
scopefunc2();
// never exists whatever the condition result is
scopefunc3();
}
}
obj.testfunc("value");
}
```

**Actual Output**

```javascript
window.onload = function() {
({
testfunc: function c(a) {
if ("test1" === a) var b = function() {
console.log(), console.log("this is scope func 2")
};
scopefunc1(), b(), scopefunc3()
}
}).testfunc("value")
};
```

**Expected Output**

```js
window.onload = function() {
({
testfunc: function c(a) {
if ("test1" === a) {
function scopefun1(){} ; var scopefunc3 = () => {}; // i ignore the function content
};
scopefunc1(), b(), scopefunc3()
}
}).testfunc("value")
};
```

**Stack Trace**

If applicable,

```

```

**Configuration**

How are you using babel-minify?

* babel-preset-minify in babelrc

"@babel/cli": "^7.1.2",
"@babel/core": "^7.1.2",
"@babel/plugin-transform-async-to-generator": "^7.1.0",
"@babel/preset-env": "^7.1.0",
"babel-loader": "^8.0.4",
"babel-plugin-transform-remove-console": "^6.9.4",
"babel-plugin-transform-runtime": "^6.23.0",
"babel-polyfill": "^6.26.0"

babelrc:

module.exports = {
"presets": [['@babel/preset-env', {
modules: false,
useBuiltIns: 'entry'
}],
"minify"
],
"plugins": [
"@babel/plugin-transform-async-to-generator"
]
}

**Possible solution**
Function should be usable in the same scope, may be there's look like a bad code style, but it's very safty for compile old javascript file. I'm using babel minify to compile old project which using requirejs, i hope there's a config option can set the loose true, and safty compile the code into a runnable minify code.

**Additional context**
node v 8.4.0
UBuntu 16.04 LTS

Start with the linked reproduction repository and the supplied babel-preset-minify configuration, then compare the original and actual output for obj.testfunc. Confirm the intended behavior for scopefunc1, scopefunc2, and scopefunc3 and reproduce the issue before investigating a fix. Done means the minified output preserves the requested function behavior and the reproduction passes.

Written by the indexing model from the issue text.