[perl #123711] Fix crash with 0-5x-l{0}

[perl #123711] Fix crash with 0-5x-l{0}

perl-5.8.0-117-g6f33ba7, which added the XTERMORDORDOR hack, did not
change the leftbracket code to treat XTERMORDORDOR the same way as
XTERM, so -l {0} and getc {0} (among other ops) were treating {...} as
a block, rather than an anonymous hash.  This was not, however, being
turned into a real block with enter/leave ops to protect the stack,
so the nextstate op was corrupting the stack and possibly freeing mor-
tals in use.

This commit makes the leftbracket code check for XTERMORDORDOR and
treat it like XTERM, so that -l {0} once more creates an anonymous
hash.  There is really no way to get to that hash, though, so all I
can test for is the crash.