Fix conversion of old muzzle flash to new type (scp-fs2open#6972)

Fixes the updated name of `Pixel Size At Emitter`

Author: wookieejedi

code/weapon/muzzleflash.cpp

@@ -194,7 +194,7 @@ static void convert_mflash_to_particle() {
 				bm_load_animation(blob.name));
 
 			if (Min_pizel_size_muzzleflash > 0) {
-				subparticles.back().m_modular_curves.add_curve("Apparent Visual Size At Emitter", particle::ParticleEffect::ParticleCurvesOutput::RADIUS_MULT, scaling_curve);
+				subparticles.back().m_modular_curves.add_curve("Pixel Size At Emitter", particle::ParticleEffect::ParticleCurvesOutput::RADIUS_MULT, scaling_curve);
 			}
 		}