[Interpreter] Register conversion fix and test.

src/interpreter/bytecode-array-builder.h

Index: src/interpreter/bytecode-array-builder.h
diff --git a/src/interpreter/bytecode-array-builder.h b/src/interpreter/bytecode-array-builder.h
index 70b881596419c1f6e1f850e7e88a7120c75e3648..c4ab816665800393986f0edcc565af3b7a51b0a9 100644
--- a/src/interpreter/bytecode-array-builder.h
+++ b/src/interpreter/bytecode-array-builder.h
@@ -84,7 +84,9 @@ class Register {
 
   int index() { return index_; }
   uint8_t ToOperand() { return static_cast<uint8_t>(-index_); }
-  static Register FromOperand(uint8_t operand) { return Register(-operand); }
+  static Register FromOperand(uint8_t operand) {
+    return Register(-static_cast<int8_t>(operand));
+  }
 
  private:
   void* operator new(size_t size);