Fix formatter error.

Change-Id: If1863ddd30dae804f63a7d511b4385820486fa3a
diff --git a/src/main/java/com/android/tools/r8/cf/CfPrinter.java b/src/main/java/com/android/tools/r8/cf/CfPrinter.java
index 3325219..8e5de6a 100644
--- a/src/main/java/com/android/tools/r8/cf/CfPrinter.java
+++ b/src/main/java/com/android/tools/r8/cf/CfPrinter.java
@@ -652,7 +652,7 @@
   }
 
   private void instructionIndex() {
-    if (PRINT_INSTRUCTION_INDEX) {
+    if (PRINT_INSTRUCTION_INDEX && instructionIndexSpace > 0) {
       builder.append(String.format("%" + instructionIndexSpace + "d: ", nextInstructionIndex++));
     }
   }