[9front] seq: fix infinite loop

[Sean Hinchee <henesy.dev@gmail.com>]

наб on twitter, then over e-mail (CC'd) pointed out that seq(1) in
9front with some very large inputs

For example:

    ; seq 2e16 20000000000000002

would loop forever.

After patch application, seq with the above example would print
'2e+16' once and then exit.

Patch also brings the usage message in line with the manual usage.

Patch link: http://okturing.com/src/11872/body

Inline:

--- //.git/fs/object/2af46e406bbd443ae10025777247798a685afc3c/tree/sys/src/cmd/seq.c
+++ sys/src/cmd/seq.c
@@ -11,7 +11,7 @@
 void
 usage(void)
 {
- fprint(2, "usage: seq [-fformat] [-w] [first [incr]] last\n");
+ fprint(2, "usage: seq [-w] [-fformat] [first [incr]] last\n");
  exits("usage");
 }

@@ -67,6 +67,7 @@
  default:
  goto out;
  }ARGEND
+
     out:
  if(argc<1 || argc>3)
  usage();
@@ -81,6 +82,7 @@
  }
  if(!format)
  buildfmt();
+
  if(incr > 0){
  for(val = min; val <= max; val += incr){
  n = sprint(buf, format, val);
@@ -88,6 +90,8 @@
  for(j=0; buf[j]==' '; j++)
  buf[j] ='0';
  write(1, buf, n);
+ if(val == max)
+ break;
  }
  }else{
  for(val = min; val >= max; val += incr){
@@ -96,7 +100,10 @@
  for(j=0; buf[j]==' '; j++)
  buf[j] ='0';
  write(1, buf, n);
+ if(val == max)
+ break;
  }
  }
+
  exits(0);
 }