Fix crash when loading local bundle and hot reload is enabled

Summary:
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When initializing react native module using a url pointing to local jsbundle and hot reload is enabled, bridge, is trying to initialize the feature but crashes because there is no host in a local file url.

1. Create a new project.

```sh
$ react-native init testPlanApp && cd testPlanApp
```

2. Create jsbundle.

```sh
$ react-native bundle --platform ios --dev false --entry-file index.js --bundle-output ios/main.jsbundle
```

3. Run the app and enable hot reload.
4. Enable airplane mode.
5. Close application and re-run.
6. See app crashes.

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  CATEGORY
[----------]        TYPE
[ CLI      ]   [-------------]      LOCATION
[ DOCS     ]   [ BREAKING    ]   [-------------]
[ GENERAl  ]   [ BUGFIX      ]   [-{Component}-]
[ INTERNAL ]   [ ENHANCEMENT ]   [ {File}      ]
[ IOS      ]   [ FEATURE     ]   [ {Directory} ]   |-----------|
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[----------]   [-------------]   [-------------]   |-----------|

[CATEGORY] [TYPE] [LOCATION] - MESSAGE

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 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
 [CLI] [FEATURE] [local-cli/info/info.js] - CLI easier to do things with
 [DOCS] [BUGFIX] [GettingStarted.md] - Accidentally a thing/word
 [GENERAL] [ENHANCEMENT] [Yoga] - Added new yoga thing/position
 [INTERNAL] [FEATURE] [./scripts] - Added thing to script that nobody will see
-->

[IOS] [BUGFIX] [Hot reloading] - Fix crash when loading local bundle and hot reload is enabled.
Closes https://github.com/facebook/react-native/pull/16504

Differential Revision: D6133767

Pulled By: shergin

fbshipit-source-id: 3f7668e3e8fa7e772f58420e5a8a0985a5f8e48b

React/CxxBridge/RCTCxxBridge.mm

@@ -810,7 +810,7 @@ struct RCTInstanceCallback : public InstanceCallback {
   }
 
 #if RCT_DEV
-  if (self.devSettings.isHotLoadingEnabled) {
+  if (self.devSettings.isHotLoadingAvailable && self.devSettings.isHotLoadingEnabled) {
     NSString *path = [self.bundleURL.path substringFromIndex:1]; // strip initial slash
     NSString *host = self.bundleURL.host;
     NSNumber *port = self.bundleURL.port;