Parser: ignore whitespaces in a when child.
Parser: ignore whitespaces in a when child.

This had clearly been forgotten since this is done everywhere else.

hsorby/libcellml,hsorby/libcellml,cellml/libcellml,MichaelClerx/libcellml,hsorby/libcellml,nickerso/libcellml,MichaelClerx/libcellml,MichaelClerx/libcellml,cellml/libcellml,cellml/libcellml,cellml/libcellml,nickerso/libcellml,nickerso/libcellml,nickerso/libcellml,hsorby/libcellml