Prevent division by zero in particle emitter frametime calculation

[seer-by-sentry]

Fixes CLIENT-1MP. The issue was that: Particle emitter optimization divides by zero GCD result when buffer size is zero.

• Added a check to ensure the Greatest Common Divisor (GCD) is greater than zero before calculating particle cycle time in part_emt.cpp.
• This prevents a potential division by zero error if the buffer size and burst size are degenerate (e.g., both zero).
• If GCD is zero, frametime is defaulted to 1.

This fix was generated by Seer in Sentry, triggered automatically. 👁️ Run ID: 8142266

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