aidl --dumpapi exits with correct error code

Fixing a bug that successful run of 'aidl --dumpapi' exits with
non-zero error code.

Test: m -j
Test: `aidl --dumpapi ~/temp/out.aidl
tests/android/aidl/tests/StructuredParcelable.aidl  && echo success`
shows 'success'

Change-Id: I0b7afd21dac9d2e5311021334d9f8ae3f32f85d0
diff --git a/main.cpp b/main.cpp
index 9560ea3..daaa6b5 100644
--- a/main.cpp
+++ b/main.cpp
@@ -44,10 +44,9 @@
     case Options::Task::COMPILE:
       return android::aidl::compile_aidl(options, io_delegate);
     case Options::Task::PREPROCESS:
-      if (android::aidl::preprocess_aidl(options, io_delegate)) return 0;
-      return 1;
+      return android::aidl::preprocess_aidl(options, io_delegate) ? 0 : 1;
     case Options::Task::DUMPAPI:
-      return android::aidl::dump_api(options, io_delegate);
+      return android::aidl::dump_api(options, io_delegate) ? 0 : 1;
     default:
       LOG(FATAL) << "aidl: internal error" << std::endl;
       return 1;