streaming: improve error handling

streaming: improve error handling

util-streaming-buffer.c:205:5: warning: Potential leak of memory pointed to by 'sbb2' [unix.Malloc]
    BUG_ON(sbb2->offset < sbb->len);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./suricata-common.h:290:27: note: expanded from macro 'BUG_ON'
        #define BUG_ON(x) assert(!(x))
                          ^~~~~~~~~~~~
/usr/include/assert.h:99:28: note: expanded from macro 'assert'
     ? __ASSERT_VOID_CAST (0)                                           \
                           ^
1 warning generated.