Try to clamp out fireflies (bright dots in image)

These sometimes happen - Somewhere in the renderer, something divides by
zero in some exceedingly unlikely case, and the resulting sample
contains NaNs.
It's fairly common to just clamp these out, but a proper approach would
be to actually trace where the goof happens, and fix that.

src/datatypes/color.h

@@ -103,6 +103,11 @@ static inline bool colorEquals(struct color a, struct color b) {
 	return a.red == b.red && a.green == b.green && a.blue == b.blue && a.alpha == b.alpha;
 }
 
+static inline void nan_clamp(struct color *a, struct color *b) {
+	if (a->red != a->red || a->green != a->green || a->blue != a->blue || a->alpha != a->alpha)
+		*a = *b;
+}
+
 struct color colorForKelvin(float kelvin);
 
 struct color color_from_hsl(float hue, float saturation, float lightness);

src/renderer/renderer.c

@@ -225,6 +225,8 @@ void *renderThreadInteractive(void *arg) {
 				struct color output = textureGetPixel(r->state.renderBuffer, x, y, false);
 				struct lightRay incidentRay = cam_get_ray(cam, x, y, sampler);
 				struct color sample = path_trace(&incidentRay, r->scene, r->prefs.bounces, sampler);
+
+				nan_clamp(&sample, &output);
 
 				//And process the running average
 				output = colorCoef((float)(r->state.finishedPasses - 1), output);
@@ -304,6 +306,9 @@ void *renderThread(void *arg) {
 					struct lightRay incidentRay = cam_get_ray(cam, x, y, sampler);
 					struct color sample = path_trace(&incidentRay, r->scene, r->prefs.bounces, sampler);
 
+					// Clamp out fireflies - This is probably not a good way to do that.
+					nan_clamp(&sample, &output);
+
 					//And process the running average
 					output = colorCoef((float)(threadState->completedSamples - 1), output);
 					output = colorAdd(output, sample);

src/utils/protocol/worker.c

@@ -171,6 +171,8 @@ static void *workerThread(void *arg) {
 					struct color output = textureGetPixel(r->state.renderBuffer, x, y, false);
 					struct lightRay incidentRay = cam_get_ray(cam, x, y, sampler);
 					struct color sample = path_trace(&incidentRay, r->scene, r->prefs.bounces, sampler);
+
+					nan_clamp(&sample, &output);
 
 					//And process the running average
 					output = colorCoef((float)(thread->completedSamples - 1), output);