config: add missing ret value check from getgrnam_r()

config: add missing ret value check from getgrnam_r()

Fix Unchecked return values from library, reported by Coverity tool:

CID 258287 (#1 of 1): Unchecked return value from library
(CHECKED_RETURN).
check_return: Calling getgrnam_r(value, group, buffer, 20480UL,
&group_buffer) without checking return value. This library function may
fail and return an error code.

CID 258303 (#1 of 1): Unchecked return value from library
(CHECKED_RETURN).
check_return: Calling getgrnam_r(value, group, buffer, 20480UL,
&group_buffer) without checking return value. This library function may
fail and return an error code.

Coverity expects us to check for return value from getgrnam_r(), instead
of the current for group_buffer != NULL.  Which is right, let's make
Coverity happy by moving the check to return value.

Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>