Raw explosion downgraded to tumble uses softenTumble

Getting hit by Proximines and Eggboxes at tripwire speed downgrades to a lesser version of tumble, much more forgiving.

src/p_inter.c

@@ -3457,6 +3457,7 @@ boolean P_DamageMobj(mobj_t *target, mobj_t *inflictor, mobj_t *source, INT32 da
 					case DMG_EXPLODE:
 						type = DMG_TUMBLE;
 						downgraded = true;
+						softenTumble = true;
 						break;
 					case DMG_TUMBLE:
 						softenTumble = true;