Add getItemLayout prop default for smooth fast scrolling

Author: farshed

lib/QuickScrollList.js

@@ -109,6 +109,15 @@ class FastScroll extends React.Component {
 		return prop;
 	}
 
+	itemLayout = () => {
+		const { itemHeight, getItemLayout } = this.props;
+		return getItemLayout
+			? getItemLayout
+			: (data, index) => {
+					return { length: itemHeight, offset: itemHeight * index, index };
+			  };
+	};
+
 	render() {
 		//prettier-ignore
 		const { thumbHeight, thumbStyle, scrollbarStyle, containerStyle, viewportHeight, touchAreaWidth } = this.props;
@@ -128,6 +137,7 @@ class FastScroll extends React.Component {
 					onScrollEndDrag={this.onScrollEnd}
 					showsVerticalScrollIndicator={false}
 					onScrollToIndexFailed={() => {}}
+					getItemLayout={this.itemLayout()}
 				/>
 				<Animated.View
 					style={[