#11 Up-conversion bug with '*' operator

[Dave McKain]

Expressions of type:

a - b - c * d

are returning exceptions.

The problem seems a missing * in pmathml-enhancer.xml, concretely in template local:group-left-associative-infix-mo. The line

<xsl:with-param name="elements" as="element()">

should be

<xsl:with-param name="elements" as="element()*">

Thanks to Borja Miñano for this bug report and investigation!