bug on vis(1): infinite loop caused by goto

[phillbush]

The following command makes vis(1) go through an infinite loop.

        $ printf 'a\tb' | vis -F8

The problem is a goto in usr.bin/vis/foldit.c

I think that the following diff fixes this, but I am not confident
enough.

--- a/vis/foldit.c      Fri Aug 14 14:08:47 2020
+++ b/vis/foldit.c      Fri Aug 14 14:01:15 2020
@@ -38,34 +38,37 @@ int
 foldit(char *chunk, int col, int max)
 {
        char *cp;
+       int newcol;

        /*
         * Keep track of column position. Insert hidden newline
         * if this chunk puts us over the limit.
         */
-again:
-       cp = chunk;
-       while (*cp) {
+       newcol = 0;
+       for (cp = chunk; *cp; cp++) {
                switch(*cp) {
                case '\n':
                case '\r':
-                       col = 0;
+                       newcol = col = 0;
                        break;
                case '\t':
                        col = (col + 8) & ~07;
+                       newcol = (newcol + 8) & ~07;
                        break;
                case '\b':
                        col = col ? col - 1 : 0;
+                       newcol = newcol ? newcol - 1 : 0;
                        break;
                default:
                        col++;
+                       newcol++;
                }
-               if (col > (max - 2)) {
-                       printf("\\\n");
-                       col = 0;
-                       goto again;
-               }
-               cp++;
        }
+
+       if (col > (max - 2)) {
+               printf("\\\n");
+               col = newcol;
+       }
+
        return (col);
 }