Fix for yet another assert fail of particle dmcache index.

This is totally broken, just making sure Blender does not crash and devs
can investigate other issues that are actually fixable.

source/blender/render/intern/source/convertblender.c

@@ -1258,7 +1258,7 @@ static void get_particle_uvco_mcol(short from, DerivedMesh *dm, float *fuv, int
 	/* get mcol */
 	if (sd->mcol && ELEM(from, PART_FROM_FACE, PART_FROM_VOLUME)) {
 		for (i=0; i<sd->totcol; i++) {
-			if (num != DMCACHE_NOTFOUND) {
+			if (!ELEM(num, DMCACHE_NOTFOUND, DMCACHE_ISCHILD)) {
 				MFace *mface = dm->getTessFaceData(dm, num, CD_MFACE);
 				MCol *mc = (MCol*)CustomData_get_layer_n(&dm->faceData, CD_MCOL, i);
 				mc += num * 4;