Release memory in Imagick::getConfigureOptions()

[mikhainin]

A few memleaks reported by ASAN.

it seems like MagickQueryConfigureOptions() returns not-constant memory and we will have to clean that up

$ ZEND_DONT_UNLOAD_MODULES=1 ./tests/254_getConfigureOptions.sh
Ok
==24023==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 182504 byte(s) in 44 object(s) allocated from:
    #0 0x7f53e933fbb8 in __interceptor_malloc (/lib64/libasan.so.5+0xefbb8)
    #1 0x7f53e3b2c436 in AcquireString MagickCore/string.c:107

Direct leak of 688 byte(s) in 2 object(s) allocated from:
    #0 0x7f53e933fbb8 in __interceptor_malloc (/lib64/libasan.so.5+0xefbb8)
    #1 0x7f53e39e1c89 in GetConfigureList MagickCore/configure.c:554

Indirect leak of 480 byte(s) in 44 object(s) allocated from:
    #0 0x7f53e933fbb8 in __interceptor_malloc (/lib64/libasan.so.5+0xefbb8)
    #1 0x7f53e3b2cb93 in ConstantString MagickCore/string.c:691

SUMMARY: AddressSanitizer: 183672 byte(s) leaked in 90 allocation(s).