Problem: gitRevision does not handle errors

Solution: handle errors in gitRevision

file.go

@@ -699,6 +699,9 @@ func (fp *FilePages) PageHistory(p string) ([]Revision, error) {
 		commitId := line[0:start]
 		rest := line[start+1:]
 		pageText := gitRevision(fp.dirname, page, commitId)
+		if pageText == "" {
+			return nil, errors.New("git revision failed")
+		}
 		revisions = append(revisions, Revision{
 			Version: commitId,
 			Page:    DiffPage{Content: pageText},
@@ -727,8 +730,14 @@ func gitRevision(dirname, page, version string) string {
 	cmd.Dir = dirname
 	buf := bytes.Buffer{}
 	cmd.Stdout = &buf
-	cmd.Start()
-	cmd.Wait()
+	err := cmd.Start()
+	if err != nil {
+		return ""
+	}
+	err = cmd.Wait()
+	if err != nil {
+		return ""
+	}
 	return buf.String()
 }