dont print color warning on color reset OSC 104 without parameter

also print explicitly "(null)" when printf "%s" p=NULL.

noticed when exiting mutt: printf '\x1b]104\x07'

st.c

@@ -1865,7 +1865,10 @@ strhandle(void)
 		case 104: /* color reset, here p = NULL */
 			j = (narg > 1) ? atoi(strescseq.args[1]) : -1;
 			if (xsetcolorname(j, p)) {
-				fprintf(stderr, "erresc: invalid color %s\n", p);
+				if (par == 104 && narg <= 1)
+					return; /* color reset without parameter */
+				fprintf(stderr, "erresc: invalid color j=%d, p=%s\n",
+				        j, p ? p : "(null)");
 			} else {
 				/*
 				 * TODO if defaultbg color is changed, borders