Correct broken unaligned load/store in armv5 (#1355)

Update vendor github.com/boltdb/bolt to take care of the issue #1354.

vendor/github.com/boltdb/bolt/page.go

@@ -62,6 +62,9 @@ func (p *page) leafPageElement(index uint16) *leafPageElement {
 
 // leafPageElements retrieves a list of leaf nodes.
 func (p *page) leafPageElements() []leafPageElement {
+	if p.count == 0 {
+		return nil
+	}
 	return ((*[0x7FFFFFF]leafPageElement)(unsafe.Pointer(&p.ptr)))[:]
 }
 
@@ -72,6 +75,9 @@ func (p *page) branchPageElement(index uint16) *branchPageElement {
 
 // branchPageElements retrieves a list of branch nodes.
 func (p *page) branchPageElements() []branchPageElement {
+	if p.count == 0 {
+		return nil
+	}
 	return ((*[0x7FFFFFF]branchPageElement)(unsafe.Pointer(&p.ptr)))[:]
 }
 
@@ -139,12 +145,33 @@ func (a pgids) merge(b pgids) pgids {
 	// Return the opposite slice if one is nil.
 	if len(a) == 0 {
 		return b
-	} else if len(b) == 0 {
+	}
+	if len(b) == 0 {
 		return a
 	}
+	merged := make(pgids, len(a)+len(b))
+	mergepgids(merged, a, b)
+	return merged
+}
 
-	// Create a list to hold all elements from both lists.
-	merged := make(pgids, 0, len(a)+len(b))
+// mergepgids copies the sorted union of a and b into dst.
+// If dst is too small, it panics.
+func mergepgids(dst, a, b pgids) {
+	if len(dst) < len(a)+len(b) {
+		panic(fmt.Errorf("mergepgids bad len %d < %d + %d", len(dst), len(a), len(b)))
+	}
+	// Copy in the opposite slice if one is nil.
+	if len(a) == 0 {
+		copy(dst, b)
+		return
+	}
+	if len(b) == 0 {
+		copy(dst, a)
+		return
+	}
+
+	// Merged will hold all elements from both lists.
+	merged := dst[:0]
 
 	// Assign lead to the slice with a lower starting value, follow to the higher value.
 	lead, follow := a, b
@@ -166,7 +193,5 @@ func (a pgids) merge(b pgids) pgids {
 	}
 
 	// Append what's left in follow.
-	merged = append(merged, follow...)
-
-	return merged
+	_ = append(merged, follow...)
 }