Fix Uninitialized eq2eqid Hash

Thanks to Adeel Khan for reporting.
Fixes Instiki Issue #52.

lib/maruku/ext/math/elements.rb

@@ -9,7 +9,6 @@ def md_equation(math, label, numerate)
       math = math.gsub(reglabel, '') if label = math[reglabel, 1]
       num = nil
       if (label || numerate) && @doc # take number
-        @doc.eqid2eq ||= {}
         num = @doc.eqid2eq.size + 1
         label = "eq#{num}" unless label # TODO do id for document
       end

lib/maruku/ext/math/parsing.rb

@@ -5,6 +5,10 @@ class MDDocument
     # @return [String => MDElement]
     attr_accessor :eqid2eq
 
+    def eqid2eq
+      @eqid2eq || {}
+    end
+
     def is_math_enabled?
       get_setting :math_enabled
     end

spec/block_docs/math/Instiki_Issue_52.md

@@ -0,0 +1,21 @@
+Fixes Uninitialized eq2eqid hash
+*** Parameters: ***
+require 'maruku/ext/math';{:html_math_engine => 'itex2mml'}
+*** Markdown input: ***
+This is an unresolved equation reference (eq:xyz).
+
+*** Output of inspect ***
+md_el(:document, md_par([
+       	"This is an unresolved equation reference ",
+       	md_el(:eqref, [], {:eqid=>"xyz"}),
+       	"."
+]))
+*** Output of to_html ***
+<p>This is an unresolved equation reference (eq:xyz).</p>
+
+*** Output of to_latex ***
+This is an unresolved equation reference \eqref{xyz}.
+*** Output of to_md ***
+
+*** Output of to_s ***
+