fix: request.compiler_version is undefined (#140)

When running with buf, request.compiler_version is undefined, which
causes a TypeError when attempting to assign major, minor and patch.

Fixes #139.

src/index.ts

@@ -116,7 +116,7 @@ for (const fileDescriptor of request.proto_file) {
     }
   }
 
-  const { major = 0, minor = 0, patch = 0 } = request.compiler_version;
+  const { major = 0, minor = 0, patch = 0 } = request.compiler_version ?? {};
 
   const comments = [
     `Generated by the protoc-gen-ts.  DO NOT EDIT!`,