Fix rtl handling for color glyphs

When the run contains a mix of color and non-color glyphs, composite_color_glyphs returns the non-color glyphs unhandled in the same array. In the rtl case, the glyphs are processed from the end and the unhandled glyphs are accumulated at the end as well, and we need to move them to the beginning of the array before we return. Add the missing memmove call to do that.

Fixes: #533 (closed)