itex Endpoint Should Handle Blank TeX

Reported by Andrew Stacey

app/metal/itex.rb

@@ -16,9 +16,17 @@ class Itex
   
   def self.response(env)
     @params = Rack::Request.new(env).params
-    tex = @params['tex'].purify
-    display = @params['display'] || 'inline'
-    filter = (display  + '_filter').to_sym
+    tex = (@params['tex'] || '').purify
+    case @params['display']
+      when 'block'
+        filter = :block_filter
+      when 'inline'
+         filter = :inline_filter
+      else
+         filter = :inline_filter
+    end
+    return "<math xmlns='http://www.w3.org/1998/Math/MathML' display='" +
+        filter.to_s[/(.*?)_filter/] + "'/>" if tex.strip == ''
     estart = "<math xmlns='http://www.w3.org/1998/Math/MathML' display='inline'><merror><mtext>"
     eend = "</mtext></merror></math>"
     begin