Freeze if Gz.deflate->deflate used twice

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=1843

Reported by Andreas Lange, Roxen IS lange@roxen.com

megalon:~$ gdb ~/pike/7.2.101/bin/pike
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This GDB was configured as "sparc-sun-solaris2.8"...
(gdb) r
Starting program: /home/lange/pike/7.2.101/bin/pike
[New LWP 1]
[New LWP 2]
[New LWP 3]
[New LWP 4]
[New LWP 5]
Pike v7.2 release 101 running Hilfe v2.0 (Incremental Pike Frontend)
> function g = Gz.deflate()->deflate;
Result: deflate
> g("1");
Result: "x\234""3\4\0\0""2\0""2"
> g("2");

[Here it stops]

Program received signal SIGTERM, Terminated.
0xff36fff0 in thr_self () from /usr/lib/libthread.so.1
(gdb) bt
#0  0xff36fff0 in thr_self () from /usr/lib/libthread.so.1
#1  0xfe7d16f0 in do_deflate (buf=0xffbee968, this=0x35e828, flush=4)
    at /home/lange/Pike/7.2/src/modules/Gz/zlibmod.c:156
#2  0xfe7d1920 in gz_deflate (args=1)
    at /home/lange/Pike/7.2/src/modules/Gz/zlibmod.c:237
#3  0x49d34 in mega_apply (type=APPLY_STACK, args=1, arg1=0x2e2444,
arg2=0x1)
    at /home/lange/Pike/7.2/src/interpret.c:1228
#4  0x48164 in eval_instruction_without_debug (pc=0x307172 "\232\"\177-")
    at /home/lange/Pike/7.2/src/interpret_functions.h:1489
#5  0x4a140 in mega_apply (type=APPLY_STACK, args=0, arg1=0x0, arg2=0x2)
    at /home/lange/Pike/7.2/src/interpret.c:799

The code around this is
154:         THREADS_ALLOW();
155:         ret=deflate(& this->gz, flush);
156:         THREADS_DISALLOW();