Fix an NPE in recent code

Change-Id: I5c76edff5c3c250167d425a737b09b10e25f9f84

tools/dicttool/src/com/android/inputmethod/latin/dicttool/Diff.java

@@ -144,7 +144,9 @@ public class Diff extends Dicttool.Command {
                 System.out.println("Bigram removed: " + word + " " + attribute0.mWord + " "
                         + attribute0.mFrequency);
             }
-        } else if (null != list0) {
+            return;
+        }
+        if (null != list0) {
             for (final WeightedString attribute0 : list0) {
                 // The following tests with #equals(). The WeightedString#equals() method returns
                 // true if both the string and the frequency are the same.