Fix Memory Leak in testMessageArrayRef()

Fix Memory Leak in testMessageArrayRef()

While running virdbustest, it was found that valgrind pointed out
the following memory leaks:

==9996== 17 (8 direct, 9 indirect) bytes in 1 blocks are definitely lost in loss record 9 of 36
==9996==    at 0x4A069EE: malloc (vg_replace_malloc.c:270)
==9996==    by 0x4A06B62: realloc (vg_replace_malloc.c:662)
==9996==    by 0x4C6B587: virReallocN (viralloc.c:245)
==9996==    by 0x4C6B6AE: virExpandN (viralloc.c:294)
==9996==    by 0x4C82B54: virDBusMessageDecodeArgs (virdbus.c:907)
==9996==    by 0x4C83463: virDBusMessageDecode (virdbus.c:1141)
==9996==    by 0x402C45: testMessageArrayRef (virdbustest.c:273)
==9996==    by 0x404E71: virtTestRun (testutils.c:201)
==9996==    by 0x401C2D: mymain (virdbustest.c:479)
==9996==    by 0x4055ED: virtTestMain (testutils.c:789)
==9996==    by 0x3E6CE1ED1C: (below main) (libc-start.c:226)
==9996==
==9996== 28 (16 direct, 12 indirect) bytes in 1 blocks are definitely lost in loss record 12 of 36
==9996==    at 0x4A06BE0: realloc (vg_replace_malloc.c:662)
==9996==    by 0x4C6B587: virReallocN (viralloc.c:245)
==9996==    by 0x4C6B6AE: virExpandN (viralloc.c:294)
==9996==    by 0x4C82B54: virDBusMessageDecodeArgs (virdbus.c:907)
==9996==    by 0x4C83463: virDBusMessageDecode (virdbus.c:1141)
==9996==    by 0x402C45: testMessageArrayRef (virdbustest.c:273)
==9996==    by 0x404E71: virtTestRun (testutils.c:201)
==9996==    by 0x401C2D: mymain (virdbustest.c:479)
==9996==    by 0x4055ED: virtTestMain (testutils.c:789)
==9996==    by 0x3E6CE1ED1C: (below main) (libc-start.c:226)
==9996==

Signed-off-by: Eric Blake <eblake@redhat.com>