BLF: Make sure a struct is completely initialized.

Initialize infstream. Fixes

```
*** CID 1497282:    (UNINIT)
/builds/wireshark/wireshark/wiretap/blf.c: 506 in blf_pull_logcontainer_into_memory()
500             }
501
502             int ret = inflate(&infstream, Z_NO_FLUSH);
503             /* Z_OK should not happen here since we know how big the buffer should be */
504             if (Z_STREAM_END != ret) {
505                 ws_debug("inflate failed (return code %d) for LogContainer %d", ret, index_log_container);
>>>     CID 1497282:    (UNINIT)
>>>     Using uninitialized value "infstream.msg".
506                 if (infstream.msg != NULL) {
507                     ws_debug("inflate returned: \"%s\"", infstream.msg);
508                 }
509                 return FALSE;
510             }
511
/builds/wireshark/wireshark/wiretap/blf.c: 514 in blf_pull_logcontainer_into_memory()
508                 }
509                 return FALSE;
510             }
511
512             if (Z_OK != inflateEnd(&infstream)) {
513                 ws_debug("inflateEnd failed for LogContainer %d", index_log_container);
>>>     CID 1497282:    (UNINIT)
>>>     Using uninitialized value "infstream.msg".
514                 if (infstream.msg != NULL) {
515                     ws_debug("inflateEnd returned: \"%s\"", infstream.msg);
516                 }
517                 return FALSE;
518             }
519
/builds/wireshark/wireshark/wiretap/blf.c: 496 in blf_pull_logcontainer_into_memory()
490             infstream.avail_out = (unsigned int)tmp.real_length;
491             infstream.next_out  = buf;
492
493             /* the actual DE-compression work. */
494             if (Z_OK != inflateInit(&infstream)) {
495                 ws_debug("inflateInit failed for LogContainer %d", index_log_container);
>>>     CID 1497282:    (UNINIT)
>>>     Using uninitialized value "infstream.msg".
496                 if (infstream.msg != NULL) {
497                     ws_debug("inflateInit returned: \"%s\"", infstream.msg);
498                 }
499                 return FALSE;
500             }
501
```

wiretap/blf.c

@@ -480,10 +480,7 @@ blf_pull_logcontainer_into_memory(blf_params_t *params, guint index_log_containe
         }
 
         unsigned char *buf = g_try_malloc0((gsize)tmp.real_length);
-        z_stream infstream;
-        infstream.zalloc = Z_NULL;
-        infstream.zfree = Z_NULL;
-        infstream.opaque = Z_NULL;
+        z_stream infstream = {0};
 
         infstream.avail_in  = (unsigned int)data_length;
         infstream.next_in   = compressed_data;