fix: stop index out of range on block boundaries

Pulls in changes from 03266d0 in
upstream, without intermediate changes, and without stray println.

low/reader.go

@@ -86,7 +86,7 @@ func (r *Reader) Id(i uint16) (uint32, error) {
 	// Populate the id table as needed
 	var blockNum uint32
 	if i != 0 { // If i == 0, we go negatives causing issues with uint32s
-		blockNum = uint32(math.Ceil(float64(i)/2048)) - 1
+		blockNum = uint32(math.Ceil(float64(i+1)/2048)) - 1
 	} else {
 		blockNum = 0
 	}
@@ -129,7 +129,7 @@ func (r *Reader) fragEntry(i uint32) (fragEntry, error) {
 	// Populate the fragment table as needed
 	var blockNum uint32
 	if i != 0 { // If i == 0, we go negatives causing issues with uint32s
-		blockNum = uint32(math.Ceil(float64(i)/512)) - 1
+		blockNum = uint32(math.Ceil(float64(i+1)/512)) - 1
 	} else {
 		blockNum = 0
 	}
@@ -175,7 +175,7 @@ func (r *Reader) inodeRef(i uint32) (uint64, error) {
 	// Populate the export table as needed
 	var blockNum uint32
 	if i != 0 { // If i == 0, we go negatives causing issues with uint32s
-		blockNum = uint32(math.Ceil(float64(i)/1024)) - 1
+		blockNum = uint32(math.Ceil(float64(i+1)/1024)) - 1
 	} else {
 		blockNum = 0
 	}