sliming ghosts

From a bug report.  Green slime would slime noncorporeals.
Added missing checks.

src/uhitm.c

@@ -1642,6 +1642,7 @@ register struct attack *mattk;
 	    case AD_SLIM:
 		if (negated) break;	/* physical damage only */
 		if (!rn2(4) && !flaming(mdef->data) &&
+				!noncorporeal(mdef->data) &&
 				mdef->data != &mons[PM_GREEN_SLIME]) {
 		    You("turn %s into slime.", mon_nam(mdef));
 		    (void) newcham(mdef, &mons[PM_GREEN_SLIME], FALSE, FALSE);