Calling sound_effect() while a sound effect is playing may cause a sound problem.

[mori0091]

Describe the bug
Setting another sound effect (fewer channels) while a sound effect (more than two channels) is playing may cause a short ugly sound.

To Reproduce

1. call sound_effect(x), where x points sound clip that uses two or more channels.
2. while the x is playing, call sound_effet(y), where y points sound clip with higher priority that uses fewer channels.

Expected behavior
At the above step 2, the sound clip x stop and the y is played w/o ugly sound.

Development environment (please complete the following information):

• OS and version: Ubuntu 20.04 on WSL2
• Compiler and version: sdcc 3.8.0
• Emulator and version: openMSX 17.0, blueMSX 2.8.2
• BIOS and version: C-BIOS_MSX2+_JP 0.29, or else

Target Platform

• MSX
• MSX2
• MSX2+
• MSXturboR

Additional context