#364 math in .wikitext files fails when not in original page

[Lee Worden]

A file like

<source-file filename=mathy.wikitex>
Look at this $$\frac{a+b}{c}$$
</source-file>

displays fine in its page, but when displayed in the GetProjectFile page, the math fails to compile: "No rule to make <whatever>.latexml.html5". Presumably has something to do with inferring what page the math source file is stored on ($$..$$ fragments are implemented as source-file tags, though they don't look like them to the editor).