Segfault on `v` action for any issue in Sprints layout

**Describe the bug**
A crash on the `v` action in Sprints layout for any issue:
```
┘panic: runtime error: invalid memory address or nil pointer dereference ║ ║
[signal SIGSEGV: segmentation violation code=0x2 addr=0xa0 pc=0x102d7acd4] ║
║ ║
║ goroutine 29 [running]: ║
║ github.com/ankitpokhrel/jira-cli/internal/view.Issue.header({{0x14000b4e828, 0x17}, 0x0, {0x0, 0x0, 0x0, {0x0, 0x0, 0x0}, 0x0, ...}, ...}) ║ ║
/Users/ankitpokhrel/go/src/github.com/ankitpokhrel/jira-cli/internal/view/issue.go:203 +0x64 ║
║ github.com/ankitpokhrel/jira-cli/internal/view.Issue.fragments({{0x14000b4e828, 0x17}, 0x0, {0x0, 0x0, 0x0, {0x0, 0x0, 0x0}, 0x0, ...}, ...}) ║ ║
/Users/ankitpokhrel/go/src/github.com/ankitpokhrel/jira-cli/internal/view/issue.go:127 +0x98 ║
║ github.com/ankitpokhrel/jira-cli/internal/view.Issue.RenderedOut({{0x14000b4e828, 0x17}, 0x0, {0x0, 0x0, 0x0, {0x0, 0x0, 0x0}, 0x0, ...}, ...}, ...) ║
║ /Users/ankitpokhrel/go/src/github.com/ankitpokhrel/jira-cli/internal/view/issue.go:76 +0xac ║
║ github.com/ankitpokhrel/jira-cli/internal/view.(*SprintList).Render.func1.2({0x10306db80?, 0x0?}) ║ ║
/Users/ankitpokhrel/go/src/github.com/ankitpokhrel/jira-cli/internal/view/sprint.go:66 +0xb4 ║
║ github.com/ankitpokhrel/jira-cli/pkg/tui.(*Preview).initContents.func1.2.1(0x140001b6690, 0x2, 0x28?, 0x14000a60f50?) ║ ║
/Users/ankitpokhrel/go/src/github.com/ankitpokhrel/jira-cli/pkg/tui/preview.go:255 +0xe4 ║
║ github.com/ankitpokhrel/jira-cli/pkg/tui.(*Preview).initContents.func1.2() ║ ║
/Users/ankitpokhrel/go/src/github.com/ankitpokhrel/jira-cli/pkg/tui/preview.go:259 +0x30═════════════════════════════════════════════════════════════════════════════════════════════════════════════════════╝
Showing 20 results from board "XXX Kanban" of project "YYY" created by github.com/ankitpokhrel/jira-cli/pkg/tui.(*Preview).initContents.func1
/Users/ankitpokhrel/go/src/github.com/ankitpokhrel/jira-cli/pkg/tui/preview.go:244 +0x264
```

**Please provide following details**

1. JiraCLI Version:
```
(Version="1.3.0", GitCommit="ed84fe74f68ba1b2cf0504a931ca09a03b2c9fed", CommitDate="2023-01-02T09:59:32+00:00", GoVersion="go1.19.4", Compiler="gc", Platform="darwin/arm64")
```

Happens also on the latest git version: https://github.com/ankitpokhrel/jira-cli/commit/eef7ae96c20a26f16b26f178c07ebe7df11511ab

2. Are you using Jira cloud or on-premise jira server?
```
SERVER INFO
-----------

Version: 8.20.6
Build Number: 820006
Deployment Type: Server
Default Locale:
```

3. What operating system are you using? Also mention version.
```
macOS 13.2 ARM64
```
4. What terminal are you using? Also mention version.
```
iTerm 2 Build 3.4.19
```

**To Reproduce**

Steps to reproduce the behavior:
1. `jira sprint list`
2. Select any sprint and issue, then press `v`
3. See error

**Expected behavior**
No crash