Fix crash when mixin target cannot be found (#7)

Author: Moulberry

definition/src/main/java/org/sinytra/adapter/patch/transformer/dynfix/DynFixSyntheticInstanceof.java

@@ -37,7 +37,10 @@ public Data prepare(MethodContext methodContext) {
             && methodContext.hasInjectionPointValue("INVOKE")
             && methodContext.findCleanInjectionTarget() != null && methodContext.findDirtyInjectionTarget() != null
         ) {
-            List<AbstractInsnNode> insns = methodContext.findInjectionTargetInsns(methodContext.findCleanInjectionTarget()); 
+            List<AbstractInsnNode> insns = methodContext.findInjectionTargetInsns(methodContext.findCleanInjectionTarget());
+            if (insns.isEmpty()) {
+                return null;
+            }
             return new Data(insns.getFirst());
         }
         return null;