[MU4 Issue] DOWNLOAD_SOUNDFONT fails silently in presence of connectivity issues

[HadrienG2]

Describe the bug
If the build host has no internet connectivity, then the DOWNLOAD_SOUNDFONT feature of the CMake build system will fail silently.

To Reproduce
Steps to reproduce the behavior:

1. Clone the git repository or download and unpack a source tarball
2. Turn off internet connection
3. Run the build
4. Build seems to proceed normally, but it actually uses the soundfont bundled into the repository, not the latest version from the mirrors as one would expect

Expected behavior
The build configuration should fail with a clear error message in this configuration. If people want to take care of the soundfont download themselves, then they should turn the DOWNLOAD_SOUNDFONT CMake feature off.

Screenshots
N/A

Platform information
Should be reproducible on any supported build host.

Additional context
This bug was already present in MuseScore 3.6.2, and stems from how the soundfont download feature is implemented in CMake, which has not changed significantly in 4.x. If the first VERSION file download fails (SF_VERSION_DL_STATUS is not 0), then the script exits silently with no console output.