placeholder - use pcall to catch errors

Author: cscheid

src/resources/extensions/quarto/placeholder/placeholder.lua

@@ -25,7 +25,15 @@ return {
     if output_format == "svg" then
       result = svg64
     else
-      local mt, contents = pandoc.mediabag.fetch("https://svg2png.deno.dev/" .. svg64)
+      local pcallresult, mt, contents = pcall(function()
+        local mt, contents = pandoc.mediabag.fetch("https://svg2png.deno.dev/" .. svg64)
+        return mt, contents
+      end)
+      if not pcallresult then
+        error("Error rendering placeholder")
+        error(contents)
+        return pandoc.Str("Error rendering placeholder")
+      end
       if mt ~= "image/png" then
         error("Expected image/png but got " .. mt)
         error(contents)