detect: transforms check for 0-sized buffer

[catenacyber]

Link to redmine ticket:
https://redmine.openinfosecfoundation.org/issues/5521

Describe changes:

• transforms check for 0-sized buffer to avoid undefined behavior with a 0-sized variable length array

[codecov]

Codecov Report

Merging #7770 (bdd7d32) into master (9353b07) will increase coverage by 0.06%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #7770      +/-   ##
==========================================
+ Coverage   75.98%   76.04%   +0.06%     
==========================================
  Files         661      661              
  Lines      185764   185773       +9     
==========================================
+ Hits       141152   141274     +122     
+ Misses      44612    44499     -113     

Flag	Coverage Δ
fuzzcorpus	60.96% <50.00%> (+0.13%)	⬆️
suricata-verify	52.51% <50.00%> (-0.01%)	⬇️
unittests	60.70% <37.50%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[suricata-qa]

Information:

ERROR: QA failed on ips_afp_drop_chk.

field	test	baseline	%
	ips_afp_stats_chk
.flow.end.state.new	89454	10800	828.28%
.flow.end.tcp_liberal	249993	108000	231.48%
.tcp.reassembly_gap	794092	108000	735.27%
.app_layer.tx.ftp	248753	263520	94.4%
.app_layer.tx.dcerpc_tcp	1003806	1101600	91.12%
	generic_stats_chk
.capture.kernel_drops	4468569	5654519	79.03%
.flow.end.tcp_state.syn_sent	887	183	484.7%
.flow.end.tcp_state.syn_recv	37	52	71.15%
.tcp.segment_memcap_drop	5393	11729	45.98%
.tcp.insert_data_normal_fail	5216	11358	45.92%
.app_layer.error.smtp.gap	75	61	122.95%

Pipeline 8800
WARNING: THERE IS A KNOWN BAD BASELINE WITH PACKET DROPS. bE MINDFUL OF ANY RESULTS.

[victorjulien]

Merged in #7774, thanks!