text-freetype2: Use cached glyph advances

We had these advances laying around but didn't use them here. Loading
the glyphs from the fonts is extremely slow, so let's avoid that since
we take the time to cache these already.

plugins/text-freetype2/text-functionality.c

@@ -570,12 +570,17 @@ uint32_t get_ft2_text_width(wchar_t *text, struct ft2_source *srcdata)
 		const FT_UInt glyph_index =
 			FT_Get_Char_Index(srcdata->font_face, text[i]);
 
-		load_glyph(srcdata, glyph_index, get_render_mode(srcdata));
-
 		if (text[i] == L'\n')
 			w = 0;
 		else {
-			w += slot->advance.x >> 6;
+			if (src_glyph) {
+				// Use the cached values.
+				w += src_glyph->xadv;
+			} else {
+				load_glyph(srcdata, glyph_index,
+					   get_render_mode(srcdata));
+				w += slot->advance.x >> 6;
+			}
 			if (w > max_w)
 				max_w = w;
 		}