Fix search highlight in multi-whitespace bodies.

The way the highlight was done could get screwed up if you had multiple
whitespaces in a row. This particularly came up with messages with
multiple newlines.

test/unitTest/java/org/thoughtcrime/securesms/util/SearchUtilTest.java

@@ -23,6 +23,15 @@ public class SearchUtilTest {
     assertEquals(Arrays.asList(new Pair<>(0, 1)), result);
   }
 
+  @Test
+  public void getHighlightRanges_singleHighlightTokenWithNewLines() {
+    String                       text      = "123\n\n\nabc";
+    String                       highlight = "a";
+    List<Pair<Integer, Integer>> result    = SearchUtil.getHighlightRanges(LOCALE, text, highlight);
+
+    assertEquals(Arrays.asList(new Pair<>(6, 7)), result);
+  }
+
   @Test
   public void getHighlightRanges_multipleHighlightTokens() {
     String                       text      = "a bc";