fallback to stdin when some flags with no files present

Reference: /n/sources/patch/applied/tbl-args
Date: Sat Jan 28 17:15:10 CET 2006

--- /sys/src/cmd/tbl/t1.c	Sat Jan 28 17:15:07 2006
+++ /sys/src/cmd/tbl/t1.c	Sat Jan 28 17:30:32 2006
@@ -43,10 +43,7 @@
 	sargv = argv;
 	sargc--; 
 	sargv++;
-	if (sargc > 0) {
-		if(swapin() == 0)
-			error("flags but no input files");
-	} else {
+	if (sargc == 0 || swapin() == 0) {
 		tabin = (Biobuf*)getcore(sizeof(Biobuf), 1);
 		Binit(tabin, 0, OREAD);
 	}