Fix potential bugs (#10513)

* use e if it is an option
* potential nil so check err first
* check err first
* m == nil already checked

modules/markup/common/linkify.go

@@ -108,7 +108,7 @@ func (s *linkifyParser) Parse(parent ast.Node, block text.Reader, pc parser.Cont
 		}
 		at := bytes.IndexByte(line, '@')
 		m = []int{0, stop, at, stop - 1}
-		if m == nil || bytes.IndexByte(line[m[2]:m[3]], '.') < 0 {
+		if bytes.IndexByte(line[m[2]:m[3]], '.') < 0 {
 			return nil
 		}
 		lastChar := line[m[1]-1]