text: fix sorting in faceOrderer.sorted

faceOrderer.sorted tried to put the "primary" font first by tweaking the
"less" function in sort.Slice, but it didn't work correctly.

If item i equaled the "primary" font, less() always returned true. This
did not take into account if item j was the "primary" font, in which
case it could easily be sorted differently.

Rather than adding another special case for that, which I couldn't
convince myself was actually correct in every case, I just searched for
the "primary" font and moved it to the front of the slice, and then
omitted the first item of the slice from the rest of the sorting.

Signed-off-by: Larry Clapp <larry@theclapp.org>

text/gotext.go

@@ -221,12 +221,21 @@ func (c *faceOrderer) fontForStyle(font Font) (Font, bool) {
 // faces returns a slice of faces with primary as the first element and
 // the remaining faces ordered by insertion order.
 func (f *faceOrderer) sorted(primary Font) []font.Face {
-	sort.Slice(f.fonts, func(i, j int) bool {
+	// If we find primary, put it first, and omit it from the below sort.
+	lowest := 0
+	for i := range f.fonts {
 		if f.fonts[i] == primary {
-			return true
+			if i != 0 {
+				f.fonts[0], f.fonts[i] = f.fonts[i], f.fonts[0]
+			}
+			lowest = 1
+			break
 		}
-		a := f.fonts[i]
+	}
-		b := f.fonts[j]
+	sorting := f.fonts[lowest:]
+	sort.Slice(sorting, func(i, j int) bool {
+		a := sorting[i]
+		b := sorting[j]
 		return f.fontDefaultOrder[a] < f.fontDefaultOrder[b]
 	})
 	for i, font := range f.fonts {