Make ReversibleSeekBar safe

app/src/main/java/com/hippo/ehviewer/widget/ReversibleSeekBar.java

@@ -45,29 +45,31 @@ public class ReversibleSeekBar extends AppCompatSeekBar {
 
     @Override
     public void draw(Canvas canvas) {
+        boolean reverse = mReverse;
         int saveCount = 0;
-        if (mReverse) {
+        if (reverse) {
             saveCount = canvas.save();
             float px = this.getWidth() / 2.0f;
             float py = this.getHeight() / 2.0f;
             canvas.scale(-1, 1, px, py);
         }
         super.draw(canvas);
-        if (mReverse) {
+        if (reverse) {
             canvas.restoreToCount(saveCount);
         }
     }
 
     @Override
     public boolean onTouchEvent(MotionEvent event) {
+        boolean reverse = mReverse;
         float x = 0.0f, y = 0.0f;
-        if (mReverse) {
+        if (reverse) {
             x = event.getX();
             y = event.getY();
             event.setLocation(getWidth() - x, y);
         }
         boolean result = super.onTouchEvent(event);
-        if (mReverse) {
+        if (reverse) {
             event.setLocation(x, y);
         }
         return result;