TOOLS/zsh.pl: die if we can't parse main options

This will catch cases where mpv runs without error, but the
--list-options output isn't what we expect. Otherwise, we'll make a
broken completion file that will result in cryptic errors when pressing
tab, like:

_mpv:18: command not found: *:files:->mfiles

That's been the case for most of the zsh completion issues we've had
reported, that I can remember.

Also make uninitialized variable access fatal so that failures to parse
other options will also make the script die eventually, albeit with a
less nice message.

TOOLS/zsh.pl

@@ -4,11 +4,14 @@
 
 use strict;
 use warnings;
+use warnings FATAL => 'uninitialized';
 
 my $mpv = $ARGV[0] || 'mpv';
 
 my @opts = parse_main_opts('--list-options', '^ (\-\-[^\s\*]*)\*?\s*(.*)');
 
+die "Couldn't find any options" unless (@opts);
+
 my @ao = parse_opts('--ao=help', '^  ([^\s\:]*)\s*: (.*)');
 my @vo = parse_opts('--vo=help', '^  ([^\s\:]*)\s*: (.*)');