update-book2: avoid bogus warnings about missing images

When an image is not found in the new-style location (i.e. in the
`images/` folder at the top level of the worktree), we want to fall back
to the old-style location _and not warn anybody about it_!

Signed-off-by: Johannes Schindelin <[email protected]>

script/update-book2.rb

@@ -196,7 +196,7 @@ def genbook(language_code, &get_content)
       end
 
       images.each do |path|
-        content = get_content.call(path)
+        content = get_content.call(path, :gently => true)
         csection.saveImage(path, content)
       rescue Errno::ENOENT
         begin
@@ -289,10 +289,10 @@ def remote_genbook2(language_code)
 # Generate book html directly from local git repo"
 def local_genbook2(language_code, worktree_path)
   if language_code && worktree_path
-    book = genbook(language_code) do |filename|
+    book = genbook(language_code) do |filename, options={}|
       File.open(File.join(worktree_path, filename), "r") { |infile| File.read(infile) }
     rescue => e
-      puts "::error::#{filename} is missing!"
+      puts "::error::#{filename} is missing!" unless options[:gently]
       raise e
     end
     book.sha = `git -C "#{worktree_path}" rev-parse HEAD`.chomp