Avoid NPE in trimToLengthWithEllipsis().

Currently, the text paramter is annotated with @Nullable
but passing a null value will cause an NPE.

Test: atest core/tests/coretests/src/android/text/TextUtilsTest.java
Change-Id: I95a71246aa0fe3398f09cb9b4b037ca096900ad4

core/java/android/text/TextUtils.java

@@ -2173,7 +2173,7 @@ public class TextUtils {
     public static <T extends CharSequence> T trimToLengthWithEllipsis(@Nullable T text,
             @IntRange(from = 1) int size) {
         T trimmed = trimToSize(text, size);
-        if (trimmed.length() < text.length()) {
+        if (text != null && trimmed.length() < text.length()) {
             trimmed = (T) (trimmed.toString() + "...");
         }
         return trimmed;

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

@@ -792,5 +792,6 @@ public class TextUtilsTest {
         assertEquals("ABC...", TextUtils.trimToLengthWithEllipsis("ABCDEF", 3));
         assertEquals("ABC", TextUtils.trimToLengthWithEllipsis("ABC", 3));
         assertEquals("", TextUtils.trimToLengthWithEllipsis("", 3));
+        assertNull(TextUtils.trimToLengthWithEllipsis(null, 3));
     }
 }