fix: panic on gitlab create release (#2473)

Background
---
In 5bcfa9042d the condition was changed to
that it can support the new status code returned by GitLab. However, the
condition is now checked `resp != nil` and not `resp == nil` which causes
the condition not to trigger when the resp is nil and only returns an
error. We can reproduce this issue by running
`TestGitLabCreateReleaseUknownHost` test added in this commit.

Solution
---
If we look at other error handling
91a8abb2e6/internal/client/gitlab.go (L106)
we can see that we check if the `resp` is nil as well before continuing.

Added tests for the following use cases:
- When there is an error and no response was returned.
- When there is a 403 or 404 error so we expect to create a release
  first.
- When there is an unknown error (not 404, 403) we just bail.

internal/client/gitlab.go

@@ -213,7 +213,7 @@ func (c *gitlabClient) CreateRelease(ctx *context.Context, body string) (release
 	name := title
 	tagName := ctx.Git.CurrentTag
 	release, resp, err := c.client.Releases.GetRelease(projectID, tagName)
-	if err != nil && (resp != nil && resp.StatusCode != 403 && resp.StatusCode != 404) {
+	if err != nil && (resp == nil || (resp.StatusCode != 403 && resp.StatusCode != 404)) {
 		return "", err
 	}
 

internal/client/gitlab_test.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"os"
+	"strconv"
 	"strings"
 	"testing"
 	"text/template"
@@ -227,3 +228,98 @@ func TestGitLabURLsDownloadTemplate(t *testing.T) {
 		})
 	}
 }
+
+func TestGitLabCreateReleaseUknownHost(t *testing.T) {
+	ctx := context.New(config.Project{
+		Release: config.Release{
+			GitLab: config.Repo{
+				Owner: "owner",
+				Name:  "name",
+			},
+		},
+		GitLabURLs: config.GitLabURLs{
+			API: "http://goreleaser-notexists",
+		},
+	})
+	client, err := NewGitLab(ctx, "test-token")
+	require.NoError(t, err)
+
+	_, err = client.CreateRelease(ctx, "body")
+	require.Error(t, err)
+}
+
+func TestGitLabCreateReleaseReleaseNotExists(t *testing.T) {
+	notExistsStatusCodes := []int{http.StatusNotFound, http.StatusForbidden}
+
+	for _, tt := range notExistsStatusCodes {
+		t.Run(strconv.Itoa(tt), func(t *testing.T) {
+			totalRequests := 0
+			createdRelease := false
+			srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				defer r.Body.Close()
+				totalRequests++
+
+				if !strings.Contains(r.URL.Path, "releases") {
+					w.WriteHeader(http.StatusOK)
+					fmt.Fprint(w, "{}")
+					return
+				}
+
+				// Check if release exists
+				if r.Method == http.MethodGet {
+					w.WriteHeader(tt)
+					fmt.Fprint(w, "{}")
+					return
+				}
+
+				// Create release if it doens't exists
+				if r.Method == http.MethodPost {
+					createdRelease = true
+					w.WriteHeader(http.StatusOK)
+					fmt.Fprint(w, "{}")
+					return
+				}
+
+				require.FailNow(t, "should not reach here")
+			}))
+			defer srv.Close()
+
+			ctx := context.New(config.Project{
+				GitLabURLs: config.GitLabURLs{
+					API: srv.URL,
+				},
+			})
+			client, err := NewGitLab(ctx, "test-token")
+			require.NoError(t, err)
+
+			_, err = client.CreateRelease(ctx, "body")
+			require.NoError(t, err)
+			require.True(t, createdRelease)
+			require.Equal(t, 3, totalRequests)
+		})
+	}
+}
+
+func TestGitLabCreateReleaseUnkownHTTPError(t *testing.T) {
+	totalRequests := 0
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		totalRequests++
+		defer r.Body.Close()
+
+		w.WriteHeader(http.StatusUnprocessableEntity)
+		fmt.Fprint(w, "{}")
+	}))
+	defer srv.Close()
+
+	ctx := context.New(config.Project{
+		GitLabURLs: config.GitLabURLs{
+			API: srv.URL,
+		},
+	})
+	client, err := NewGitLab(ctx, "test-token")
+	require.NoError(t, err)
+
+	_, err = client.CreateRelease(ctx, "body")
+	require.Error(t, err)
+	require.Equal(t, 2, totalRequests)
+}