Fix compilation and CI

ubuntu-latest s390x CI doesn't like snapshot bigger than 262144 bytes.

Fix an error found by fuzz CI

```
=================================================================
==55399==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000008 (pc 0x561e41cb684d bp 0x7ffd54ce3650 sp 0x7ffd54ce3520 T0)
==55399==The signal is caused by a READ memory access.
==55399==Hint: address points to the zero page.
    #0 0x561e41cb684d in ndpi_network_ptree_match /home/ivan/svnrepos/nDPI/src/lib/ndpi_main.c:2321:41
    ntop#1 0x561e41d30879 in ndpi_guess_undetected_protocol /home/ivan/svnrepos/nDPI/src/lib/ndpi_main.c:7767:8
    ntop#2 0x561e41ca804d in LLVMFuzzerTestOneInput /home/ivan/svnrepos/nDPI/fuzz/fuzz_config.cpp:104:5
    ntop#3 0x561e41bb96a0 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) (/home/ivan/svnrepos/nDPI/fuzz/fuzz_config+0x4726a0) (BuildId: d4741c753aafe7c0df2681a592b7df16b38240e9)
    ntop#4 0x561e41ba3c2f in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) (/home/ivan/svnrepos/nDPI/fuzz/fuzz_config+0x45cc2f) (BuildId: d4741c753aafe7c0df2681a592b7df16b38240e9)
    ntop#5 0x561e41ba96f6 in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) (/home/ivan/svnrepos/nDPI/fuzz/fuzz_config+0x4626f6) (BuildId: d4741c753aafe7c0df2681a592b7df16b38240e9)
    ntop#6 0x561e41bd22e2 in main (/home/ivan/svnrepos/nDPI/fuzz/fuzz_config+0x48b2e2) (BuildId: d4741c753aafe7c0df2681a592b7df16b38240e9)
    ntop#7 0x7f94f0e5c082 in __libc_start_main /build/glibc-SzIz7B/glibc-2.31/csu/../csu/libc-start.c:308:16
    ntop#8 0x561e41b9eb0d in _start (/home/ivan/svnrepos/nDPI/fuzz/fuzz_config+0x457b0d) (BuildId: d4741c753aafe7c0df2681a592b7df16b38240e9)
```

src/include/ndpi_typedefs.h

@@ -1588,8 +1588,8 @@ struct ndpi_flow_struct {
 _Static_assert(sizeof(((struct ndpi_flow_struct *)0)->protos) <= 210,
                "Size of the struct member protocols increased to more than 210 bytes, "
                "please check if this change is necessary.");
-_Static_assert(sizeof(struct ndpi_flow_struct) <= 938,
-               "Size of the flow struct increased to more than 928 bytes, "
+_Static_assert(sizeof(struct ndpi_flow_struct) <= 944,
+               "Size of the flow struct increased to more than 944 bytes, "
                "please check if this change is necessary.");
 #endif
 #endif

src/lib/ndpi_main.c

@@ -2304,6 +2304,9 @@ u_int16_t ndpi_network_ptree_match(struct ndpi_detection_module_struct *ndpi_str
   ndpi_prefix_t prefix;
   ndpi_patricia_node_t *node;
 
+  if(!ndpi_str->protocols_ptree)
+    return(NDPI_PROTOCOL_UNKNOWN);
+
   if(ndpi_str->ndpi_num_custom_protocols == 0) {
     /*
       In case we don't have defined any custom protocol we check the ptree