Fix NPE in FTS when snippet is null.

src/org/thoughtcrime/securesms/ConversationListItem.java

@@ -319,9 +319,13 @@ public class ConversationListItem extends RelativeLayout
                                      @Nullable String value,
                                      @Nullable String highlight)
   {
-    value = value != null ? value.replaceAll("\n", " ") : null;
+    if (value == null) {
+      return new SpannableString("");
+    }
+
+    value = value.replaceAll("\n", " ");
 
-    if (value == null || highlight == null) {
+    if (highlight == null) {
       return new SpannableString(value);
     }