plug a memory leak in diff(1)

[Stefan Sperling]

Line buffers allocated in preadline() were never freed.

ok?

Index: diffreg.c
===================================================================
RCS file: /cvs/src/usr.bin/diff/diffreg.c,v
retrieving revision 1.91
diff -u -p -r1.91 diffreg.c
--- diffreg.c   1 Mar 2016 20:57:35 -0000       1.91
+++ diffreg.c   2 Apr 2018 17:37:34 -0000
@@ -966,7 +966,6 @@ restart:
        if (diff_format != D_IFDEF && a > b && c > d)
                return;
        if (ignore_pats != NULL) {
-               char *line;
                /*
                 * All lines in the change, insert, or delete must
                 * match an ignore pattern for the change to be
@@ -974,18 +973,24 @@ restart:
                 */
                if (a <= b) {           /* Changes and deletes. */
                        for (i = a; i <= b; i++) {
-                               line = preadline(fileno(f1),
+                               char *line = preadline(fileno(f1),
                                    ixold[i] - ixold[i - 1], ixold[i - 1]);
-                               if (!ignoreline(line))
+                               if (!ignoreline(line)) {
+                                       free(line);
                                        goto proceed;
+                               }
+                               free(line);
                        }
                }
                if (a > b || c <= d) {  /* Changes and inserts. */
                        for (i = c; i <= d; i++) {
-                               line = preadline(fileno(f2),
+                               char *line = preadline(fileno(f2),
                                    ixnew[i] - ixnew[i - 1], ixnew[i - 1]);
-                               if (!ignoreline(line))
+                               if (!ignoreline(line)) {
+                                       free(line);
                                        goto proceed;
+                               }
+                               free(line);
                        }
                }
                return;