fix recalc of byte offsets

uncrust.go

@@ -83,19 +83,24 @@ func main() {
 
 	// We have to calculate the rune position from the byte position.
 	rcount := 0
-	idx := 0
+	sidx, eidx := 0, 0
 	for p := range before {
-		for i := range edits[idx:] {
-			if edits[i].Start == p {
-				edits[i].Start = rcount
+		for i := range edits[sidx:] {
+			if edits[sidx+i].Start == p {
+				edits[sidx+i].Start = rcount
+				sidx += i
+				break
 			}
-			if edits[i].End == p {
-				edits[i].End = rcount
-				idx++
+		}
+		for i := range edits[eidx:] {
+			if edits[i+eidx].End == p {
+				edits[i+eidx].End = rcount
+				eidx += i
+				break
 			}
 		}
 		rcount++
-		if idx == len(edits) {
+		if eidx == len(edits) {
 			break
 		}
 	}
@@ -114,7 +119,7 @@ func main() {
 		addr := fmt.Sprintf("#%d,#%d", edit.Start, edit.End)
 		e = win.Addr(addr)
 		if e != nil {
-			log.Fatalf("error writing to acme/%d/addr: %s\n", wid, e)
+			log.Fatalf("error writing %q to acme/%d/addr: %s\n", addr, wid, e)
 		}
 		win.Write("data", []byte(edit.New))
 	}