build fix

internal/shop.cm

@@ -495,6 +495,7 @@ function resolve_mod_fn(path, pkg) {
   if (!fd.is_file(path)) { print(`path ${path} is not a file`); disrupt }
 
   var content = text(fd.slurp(path))
+  if (length(content) == 0) { print(`${path}: empty file`); disrupt }
   var content_key = stone(blob(content))
   var native_result = null
   var cached = null
@@ -1049,6 +1050,7 @@ function fetch_remote_hash(pkg) {
 // Returns the zip blob or null on failure
 function download_zip(pkg, commit_hash) {
   var cache_path = get_cache_path(pkg, commit_hash)
+  ensure_dir(global_shop_path + '/cache')
 
   var download_url = Shop.get_download_url(pkg, commit_hash)
   if (!download_url) {
@@ -1177,8 +1179,10 @@ Shop.extract = function(pkg) {
 
   var zip_blob = get_package_zip(pkg)
 
-  if (!zip_blob)
-    print("No zip blob available for " + pkg); disrupt
+  if (!zip_blob) {
+    print("No zip blob available for " + pkg)
+    disrupt
+  }
 
   // Extract zip for remote package
   install_zip(zip_blob, target_dir)