Fix nondeterminism in emulated interface method code generation

Bug: 190335834
Change-Id: I7bf98c6b9864a14f6f5e3d79dd492213ee057e74
diff --git a/src/main/java/com/android/tools/r8/ir/desugar/itf/EmulatedInterfaceProcessor.java b/src/main/java/com/android/tools/r8/ir/desugar/itf/EmulatedInterfaceProcessor.java
index cf86667..30fc05c 100644
--- a/src/main/java/com/android/tools/r8/ir/desugar/itf/EmulatedInterfaceProcessor.java
+++ b/src/main/java/com/android/tools/r8/ir/desugar/itf/EmulatedInterfaceProcessor.java
@@ -245,6 +245,8 @@
                           companionMethod.name)));
         }
       }
+    } else {
+      assert extraDispatchCases.size() <= 1;
     }
     return extraDispatchCases;
   }