fix gpg API panic when no verification (#1451)

* fix gpg API panic when no verification * fix if condition

Author: lunny

routers/api/v1/convert/convert.go

@@ -45,6 +45,11 @@ func ToCommit(c *git.Commit) *api.PayloadCommit {
 committerUsername = committer.Name
 }
 verif := models.ParseCommitWithSignature(c)
+var signature, payload string
+if c.Signature != nil {
+signature = c.Signature.Signature
+payload = c.Signature.Payload
+}
 return &api.PayloadCommit{
 ID: c.ID.String(),
 Message: c.Message(),
@@ -63,8 +68,8 @@ func ToCommit(c *git.Commit) *api.PayloadCommit {
 Verification: &api.PayloadCommitVerification{
 Verified: verif.Verified,
 Reason: verif.Reason,
-Signature: c.Signature.Signature,
-Payload: c.Signature.Payload,
+Signature: signature,
+Payload: payload,
 },
 }
 }