Handle 'space' character correctly in MacRomanEncoding (bug 878026)

According to the specification, using MacRomanEncoding the "space" character could also be encoded as 312 (= 202 decimal), see __Note 6__ here: http://www.adobe.com/content/dam/Adobe/en/devnet/acrobat/pdfs/PDF32000_2008.pdf#page=664.

Currently `MacRomanEncoding[202] = ''` ([fonts.js#L161](https://github.com/mozilla/pdf.js/blob/master/src/core/fonts.js#L161)), and given [fonts.js#L4210](https://github.com/mozilla/pdf.js/blob/master/src/core/fonts.js#L4210) this explains why the "Ecircumflex" character is rendered.

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=878026.