dpkg-deb: Force the ar member name to 16 space padded chars wide

This makes the code resilient to changes to the member name strings
and guarantees it will always have the valid length, also makes it
easier to refactor later on.

dpkg-deb/build.c

@@ -448,13 +448,15 @@ void do_build(const char *const *argv) {
     thetime = time(NULL);
     if (fprintf(ar,
                 "!<arch>\n"
-                DEBMAGIC "%-12lu0     0     100644  %-10ld`\n"
+                "%-16s%-12lu0     0     100644  %-10ld`\n"
                 ARCHIVEVERSION "\n"
                 "%s"
-                ADMINMEMBER "%-12lu0     0     100644  %-10ld`\n",
+                "%-16s%-12lu0     0     100644  %-10ld`\n",
+                DEBMAGIC,
                 thetime,
                 (long)sizeof(ARCHIVEVERSION),
                 (sizeof(ARCHIVEVERSION)&1) ? "\n" : "",
+                ADMINMEMBER,
                 (unsigned long)thetime,
                 (long)controlstab.st_size) == EOF)
       werr(debar);
@@ -557,7 +559,7 @@ void do_build(const char *const *argv) {
       ohshite(_("failed to fstat tmpfile (data)"));
     if (fprintf(ar,
                 "%s"
-                "%s" "%-12lu0     0     100644  %-10ld`\n",
+                "%-16s%-12lu0     0     100644  %-10ld`\n",
                 (controlstab.st_size & 1) ? "\n" : "",
                 datamember,
                 (unsigned long)thetime,