galerautils/src/gu_mem.c realloc() bug. 'ret' nulled but not freed upon failure

from cppcheck:

<error file="galerautils/src/gu_mem.c" line="98" id="memleakOnRealloc" severity="error" msg="Common realloc mistake: 'ret' nulled but not freed upon failure"/>

<error file="tests/test_sysbench/sysbench/drivers/mysql/drv_mysql.c" line="690" id="memleakOnRealloc" severity="error" msg="Common realloc mistake: 'buf' nulled but not freed upon failure"/>

<error file="tests/test_sysbench/sysbench/drivers/oracle/drv_oracle.c" line="444" id="memleakOnRealloc" severity="error" msg="Common realloc mistake: 'buf' nulled but not freed upon failure"/>

<error file="tests/test_sysbench/sysbench/drivers/oracle/drv_oracle.c" line="655" id="memleakOnRealloc" severity="error" msg="Common realloc mistake: 'buf' nulled but not freed upon failure"/>

<error file="tests/test_sysbench/sysbench/drivers/pgsql/drv_pgsql.c" line="289" id="memleakOnRealloc" severity="error" msg="Common realloc mistake: 'buf' nulled but not freed upon failure"/>

<error file="tests/test_sysbench/sysbench/drivers/pgsql/drv_pgsql.c" line="511" id="memleakOnRealloc" severity="error" msg="Common realloc mistake: 'buf' nulled but not freed upon failure"/>