typo similar with ffa0574 (#596)

Author: pxb1988

dex-ir/src/main/java/com/googlecode/dex2jar/ir/ts/TypeTransformer.java

@@ -478,7 +478,7 @@ private static String mergeTypeEx(String a, String b) {
                 return b;
             } else { // as==bs;
                 String elementTypeA = a.substring(as);
-                String elementTypeB = a.substring(bs);
+                String elementTypeB = b.substring(bs);
                 TypeClass ta = TypeClass.clzOf(elementTypeA);
                 TypeClass tb = TypeClass.clzOf(elementTypeB);
                 if (ta.fixed && !tb.fixed) {