Place wrapper around comment as diff to catch panics (#15085) (#15086)

* Place wrapper around comment as diff to prevent panics

* propagate the panic up

Signed-off-by: Andrew Thornton <art27@cantab.net>

services/gitdiff/gitdiff.go

@@ -1282,6 +1282,16 @@ func CommentAsDiff(c *models.Comment) (*Diff, error) {
 
 // CommentMustAsDiff executes AsDiff and logs the error instead of returning
 func CommentMustAsDiff(c *models.Comment) *Diff {
+	if c == nil {
+		return nil
+	}
+	defer func() {
+		if err := recover(); err != nil {
+			stack := log.Stack(2)
+			log.Error("PANIC whilst retrieving diff for comment[%d] Error: %v\nStack: %s", c.ID, err, stack)
+			panic(fmt.Errorf("PANIC whilst retrieving diff for comment[%d] Error: %v\nStack: %s", c.ID, err, stack))
+		}
+	}()
 	diff, err := CommentAsDiff(c)
 	if err != nil {
 		log.Warn("CommentMustAsDiff: %v", err)