Fix case where block has no predecessor for StringChange.

Removes part that checks for throwing half of instruction. It's no
longer necessary. Also adds regression test.

Bug: 21902684

(cherry-picked from commit 3e91a44bc9063f7f69b5415e3cf162991f73283f)

Change-Id: I8d7308ff227816fb475341c2b74ed84d5695a2f5
diff --git a/test/800-smali/src/Main.java b/test/800-smali/src/Main.java
index ab4457e..7280d45 100644
--- a/test/800-smali/src/Main.java
+++ b/test/800-smali/src/Main.java
@@ -88,6 +88,7 @@
         testCases.add(new TestCase("b/21873167", "B21873167", "test", null, null, null));
         testCases.add(new TestCase("b/21614284", "B21614284", "test", new Object[] { null },
             new NullPointerException(), null));
+        testCases.add(new TestCase("b/21902684", "B21902684", "test", null, null, null));
     }
 
     public void runTests() {