reset attribute to previous value as counter is only incremented when…

… there is a title (#317)

README.adoc

@@ -1,6 +1,9 @@
 = IntelliJ AsciiDoc Plugin
 Alexander Schwartz
 :experimental:
+:url-ci-travis: https://travis-ci.org/asciidoctor/asciidoctor-intellij-plugin
+
+image::https://api.travis-ci.org/asciidoctor/asciidoctor-intellij-plugin.svg?branch=master[link={url-ci-travis}]
 
 A plugin for the IntelliJ platform (IntelliJ IDEA, RubyMine, etc) that provides support for the http://www.asciidoc.org[AsciiDoc] markup language.
 To support the authors of Asciidoctor, please consider supporting us via https://opencollective.com/asciidoctor[OpenCollective].

src/main/resources/plantuml-png-patch.rb

@@ -10,10 +10,10 @@ module SvgToPngHack
   def process(parent, reader_or_target, attributes)
     # render as SVG to be used for save-as functionality
     attributes['format'] = 'svg'
-    super(parent, reader_or_target, attributes)
-    # rewind figure-number for second call, otherwise it will be incremented twice
+    # rewind figure-number for second call (note that it will only be incremented if the diagram has a title)
     fignum = parent.document.attr('figure-number')
-    parent.document.set_attr('figure-number', fignum - 1)
+    super(parent, reader_or_target, attributes)
+    parent.document.set_attr('figure-number', fignum)
     # render a second time for PNG to be used in preview
     attributes['format'] = 'png'
     super(parent, reader_or_target, attributes)