Noise: Fix PcgRandom::randNormalDist() when range contains negative numbers

This fixes an issue with erroneous float-to-int rounding that resulted in
truncation toward 0, causing a biased distribution.

src/noise.cpp

@@ -148,7 +148,7 @@ s32 PcgRandom::randNormalDist(s32 min, s32 max, int num_trials)
 	s32 accum = 0;
 	for (int i = 0; i != num_trials; i++)
 		accum += range(min, max);
-	return ((float)accum / num_trials) + 0.5f;
+	return round((float)accum / num_trials);
 }
 
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