Fix Layout.primaryIsTrailingPreviousAllLineOffsets

The CL fixes a crash in Layout.primaryIsTrailingPreviousAllLineOffsets.
The crash was happening when the method was called for a line beginning
with an empty bidi run. This could happen, for example, for empty text -
I was unable to find any other case. The CL improves the existing test
for the method with this case, which was previously crashing.

The CL also fixes a potential crash in getLineHorizontals. However, this
bug could never happen as in the current code path clamped is always
false (and kept as parameter for parity with getHorizontal).

Bug: 135444178
Test: atest FrameworksCoreTests:android.text.LayoutTest\#testPrimaryIsTrailingPrevious
Change-Id: I47157abe1d74675884734e3810628a566e40c1b4

core/java/android/text/Layout.java

@@ -1122,6 +1122,9 @@ public boolean[] primaryIsTrailingPreviousAllLineOffsets(int line) {
             if (limit > lineEnd) {
                 limit = lineEnd;
             }
+            if (limit == start) {
+                continue;
+            }
             level[limit - lineStart - 1] =
                     (byte) ((runs[i + 1] >>> RUN_LEVEL_SHIFT) & RUN_LEVEL_MASK);
         }
@@ -1220,8 +1223,8 @@ private float getHorizontal(int offset, boolean trailing, int line, boolean clam
     }
 
     /**
-     * Computes in linear time the results of calling
-     * #getHorizontal for all offsets on a line.
+     * Computes in linear time the results of calling #getHorizontal for all offsets on a line.
+     *
      * @param line The line giving the offsets we compute information for
      * @param clamped Whether to clamp the results to the width of the layout
      * @param primary Whether the results should be the primary or the secondary horizontal
@@ -1257,7 +1260,7 @@ private float[] getLineHorizontals(int line, boolean clamped, boolean primary) {
         TextLine.recycle(tl);
 
         if (clamped) {
-            for (int offset = 0; offset <= wid.length; ++offset) {
+            for (int offset = 0; offset < wid.length; ++offset) {
                 if (wid[offset] > mWidth) {
                     wid[offset] = mWidth;
                 }

core/tests/coretests/src/android/text/LayoutTest.java

@@ -743,6 +743,9 @@ public void testPrimaryIsTrailingPrevious() {
         assertPrimaryIsTrailingPrevious(
                 RTL + LRI + RTL + LTR + PDI + RTL,
                 new boolean[]{false, false, true, false, false, false, false});
+        assertPrimaryIsTrailingPrevious(
+                "",
+                new boolean[]{false});
     }
 }