Early exit if the target region is empty

Bug: 193849901
Test: atest StaticLayoutBidiTouchTest
Change-Id: I55f04068a6e5b353867d50742356c272d28886b3

core/java/android/text/TextLine.java

@@ -782,7 +782,7 @@ public class TextLine {
 
         int spanStart = runStart;
         int spanLimit;
-        if (mSpanned == null) {
+        if (mSpanned == null || runStart == runLimit) {
             spanLimit = runLimit;
         } else {
             int target = after ? offset + 1 : offset;