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/expected.txt b/test/800-smali/expected.txt
index 6c00c82..c762603 100644
--- a/test/800-smali/expected.txt
+++ b/test/800-smali/expected.txt
@@ -20,4 +20,5 @@
 b/21863767
 b/21873167
 b/21614284
+b/21902684
 Done!