perror_nomsg: don't print extra colon

losetup: print name of loop device in error messages

libbb/verror_msg.c

@@ -45,8 +45,10 @@ void bb_verror_msg(const char *s, va_list p, const char* strerr)
 	msg[applet_len - 2] = ':';
 	msg[applet_len - 1] = ' ';
 	if (strerr) {
-		msg[used++] = ':';
-		msg[used++] = ' ';
+		if (s[0]) { /* not perror_nomsg? */
+			msg[used++] = ':';
+			msg[used++] = ' ';
+		}
 		strcpy(&msg[used], strerr);
 		used += strerr_len;
 	}