"Failed to export flamegraph: image is empty".

[RokeJulianLockhart]

Describe the bug

I'm unable to export a flamegraph .BMP.

To Reproduce

1. Install https://kojipkgs.fedoraproject.org//packages/dolphin/24.02.2/2.fc40/x86_64/dolphin-24.02.2-2.fc40.x86_64.rpm from https://koji.fedoraproject.org/koji/rpminfo?rpmID=38381846

2. cd "$HOME" # so that the last command works as expected
   perf record --call-graph dwarf dolphin && `
   hotspot '$HOME/perf.data'

3. Attempt to export a flamgraph bitmap.

4. Save the image via the KDE File Picker (I presume via the XDG portal).

Expected behavior

The .BMP should be saved.

Screenshots

1. 

2. 

Version Info (please complete the following information):

Linux Kernel version	https://kojipkgs.fedoraproject.org//packages/kernel/6.8.9/300.fc40/x86_64/kernel-6.8.9-300.fc40.x86_64.rpm from https://koji.fedoraproject.org/koji/rpminfo?rpmID=38509280
perf version	https://kojipkgs.fedoraproject.org//packages/kernel-tools/6.5.4/300.fc39/x86_64/bpftool-6.5.4-300.fc39.x86_64.rpm from https://koji.fedoraproject.org/koji/rpminfo?rpmID=35951581
Hotspot version (AppImage? self-compiled?)	https://kojipkgs.fedoraproject.org//packages/hotspot/1.4.1/5.fc40/x86_64/hotspot-1.4.1-5.fc40.x86_64.rpm from https://koji.fedoraproject.org/koji/rpminfo?rpmID=37327082
If self-compiled Hotspot, what version of elfutils	Not self-compiled.

Additional context

1. I need this feature for https://discuss.kde.org/t/dolphin-struggles-to-load-directories-which-contain-many-files/15450/10?u=rokejulianlockhart
2. This feature appears to have been added in https://github.com/KDAB/hotspot/issues/45#event-2927708114

[lievenhey]

You need to open the flamegraph tab first, otherwise the image is not rendered and thus cannot be saved.

[RokeJulianLockhart]

https://github.com/KDAB/hotspot/issues/637#issuecomment-2111910858

@lievenhey, isn't that worth explaining in the relevant dialog window, then?

[lievenhey]

that is already done https://github.com/KDAB/hotspot/pull/588