fix crash on some android 6 devices, (image can't be null)

lib/index.js

@@ -181,17 +181,25 @@ export default class PhoneInput extends Component {
   render() {
     const { iso2, inputValue, disabled } = this.state;
     const TextComponent = this.props.textComponent || TextInput;
+    const FlagSource = Flags.get(iso2);
     return (
       <View style={[styles.container, this.props.style]}>
         <TouchableWithoutFeedback
           onPress={this.onPressFlag}
           disabled={disabled}
         >
-          <Image
-            source={Flags.get(iso2)}
-            style={[styles.flag, this.props.flagStyle]}
-            onPress={this.onPressFlag}
-          />
+          {
+            !!FlagSource ?(
+              <Image
+                source={FlagSource}
+                style={[styles.flag, this.props.flagStyle]}
+                onPress={this.onPressFlag}
+              />
+            ) :
+              <View
+                style={[styles.flag, this.props.flagStyle]}
+              />
+          }
         </TouchableWithoutFeedback>
         <View style={{ flex: 1, marginLeft: this.props.offset || 10 }}>
           <TextComponent