osmo-sim-test.c: Fix rmsg check

we wanted to check for !rmsg, but used to check for !msg, missing error
returns from read_record_nr().

Change-Id: I79b6a94b1aa947c8329317b0626865c3cd4159c1
Fixes: Coverity CID 57672

utils/osmo-sim-test.c

@@ -334,7 +334,7 @@ static int dump_file(struct osim_chan_hdl *chan, uint16_t fid)
 	case EF_TYPE_RECORD_FIXED:
 		for (i = 0; i < ffdd.num_rec; i++) {
 			rmsg = read_record_nr(chan, i+1, ffdd.rec_len);
-			if (!msg)
+			if (!rmsg)
 				return -EIO;
 			printf("SW: %s\n", osim_print_sw(chan->card, msgb_apdu_sw(msg)));
 			printf("Rec %03u: %s\n", i+1,