Set LocalBranch even if the git config fails

acceptance/testdata/pr/pr-create-without-upstream-config.txtar

@@ -0,0 +1,27 @@
+# This test is the same as pr-create-basic, except that the git push doesn't include the -u argument
+# This causes a git config read to fail during gh pr create, but it should not be fatal
+
+# Use gh as a credential helper
+exec gh auth setup-git
+
+# Create a repository with a file so it has a default branch
+exec gh repo create $ORG/$SCRIPT_NAME-$RANDOM_STRING --add-readme --private
+
+# Defer repo cleanup
+defer gh repo delete --yes $ORG/$SCRIPT_NAME-$RANDOM_STRING
+
+# Clone the repo
+exec gh repo clone $ORG/$SCRIPT_NAME-$RANDOM_STRING
+
+# Prepare a branch to PR
+cd $SCRIPT_NAME-$RANDOM_STRING
+exec git checkout -b feature-branch
+exec git commit --allow-empty -m 'Empty Commit'
+exec git push origin feature-branch
+
+# Create the PR
+exec gh pr create --title 'Feature Title' --body 'Feature Body'
+
+# Check the PR is indeed created
+exec gh pr view
+stdout 'Feature Title'

git/client.go

@@ -378,6 +378,8 @@ func (c *Client) lookupCommit(ctx context.Context, sha, format string) ([]byte,
 
 // ReadBranchConfig parses the `branch.BRANCH.(remote|merge|gh-merge-base)` part of git config.
 func (c *Client) ReadBranchConfig(ctx context.Context, branch string) (cfg BranchConfig) {
+	cfg.LocalName = branch
+
 	prefix := regexp.QuoteMeta(fmt.Sprintf("branch.%s.", branch))
 	args := []string{"config", "--get-regexp", fmt.Sprintf("^%s(remote|merge|%s)$", prefix, MergeBaseConfig)}
 	cmd, err := c.Command(ctx, args...)
@@ -389,7 +391,6 @@ func (c *Client) ReadBranchConfig(ctx context.Context, branch string) (cfg Branc
 		return
 	}
 
-	cfg.LocalName = branch
 	for _, line := range outputLines(out) {
 		parts := strings.SplitN(line, " ", 2)
 		if len(parts) < 2 {