Correctly handle non-ASCII runes in patterns (fixes #54)

When matching a row we calculate an index into the string, and this
index was in runes. However when slicing the string Go uses byte
indexes. This change tracks both, using the rune count to determine the
correct length and the byte index to slice the string.

glob_test.go

@@ -162,6 +162,16 @@ func TestGlob(t *testing.T) {
 
 		glob(true, pattern_prefix_suffix, fixture_prefix_suffix_match),
 		glob(false, pattern_prefix_suffix, fixture_prefix_suffix_mismatch),
+
+		glob(true, "155ö", "155ö"),
+		glob(true, "1?5ö", "155ö"), // <-
+		glob(true, "1?ö5", "15ö5"),
+		glob(true, "155helloö", "155helloö"),
+		glob(true, "1?5helloö", "155helloö"), // <-
+		glob(true, "1?ö5hello", "15ö5hello"),
+		glob(true, "1?5heöllo", "155heöllo"),
+		glob(true, "1ö?5", "1ö55"), // <-
+		glob(true, "ö1?5", "ö155"),
 	} {
 		t.Run("", func(t *testing.T) {
 			g := MustCompile(test.pattern, test.delimiters...)

match/row.go

@@ -2,6 +2,7 @@ package match
 
 import (
 	"fmt"
+	"unicode/utf8"
 )
 
 type Row struct {
@@ -23,19 +24,21 @@ func (self Row) matchAll(s string) bool {
 	for _, m := range self.Matchers {
 		length := m.Len()
 
-		var next, i int
-		for next = range s[idx:] {
-			i++
-			if i == length {
+		var runeCount, byteIdx int
+		var r rune
+		for _, r = range s[idx:] {
+			runeCount++
+			byteIdx += utf8.RuneLen(r)
+			if runeCount == length {
 				break
 			}
 		}
 
-		if i < length || !m.Match(s[idx:idx+next+1]) {
+		if runeCount < length || !m.Match(s[idx:idx+byteIdx]) {
 			return false
 		}
 
-		idx += next + 1
+		idx += byteIdx
 	}
 
 	return true