ch: Avoid memory leak in virCHProcessEvents()

ch: Avoid memory leak in virCHProcessEvents()

The aim of virCHProcessEvents() is to read data (in JSON format)
from CH monitor and then process them. To parse incoming data
virJSONValueFromString() is used. But the corresponding
virJSONValue is freed only when processing of an even succeeds.
If processing an event fails, then the memory is not freed
leading to a memory leak.

334 (24 direct, 310 indirect) bytes in 1 blocks are definitely lost in loss record 1,975 of 2,040
   at 0x4919EF3: calloc (vg_replace_malloc.c:1675)
   by 0x4FEB249: g_malloc0 (in /usr/lib64/libglib-2.0.so.0.8400.3)
   by 0x4A66162: virJSONValueNewObject (virjson.c:533)
   by 0x4A67E74: virJSONValueFromJsonC (virjson.c:1413)
   by 0x4A681A5: virJSONValueFromString (virjson.c:1484)
   by 0xB8CD9D7: virCHProcessEvents (ch_events.c:179)
   by 0xB8CDCDC: virCHReadProcessEvents (ch_events.c:251)
   by 0xB8CDEBB: virCHEventHandlerLoop (ch_events.c:284)
   by 0x4AC1EB4: virThreadHelper (virthread.c:256)
   by 0x5441DE3: start_thread (in /usr/lib64/libc.so.6)
   by 0x54C25F3: clone (in /usr/lib64/libc.so.6)

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>