Fix some errors found by fuzzers (#2078)

Fix compilation on Windows.
"dirent.h" file has been taken from https://github.com/tronkko/dirent/

Fix Python bindings

Fix some warnings with x86_64-w64-mingw32-gcc:
```
protocols/dns.c: In function ‘ndpi_search_dns’:
protocols/dns.c:775:41: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
  775 |       unsigned long first_element_len = (unsigned long)dot - (unsigned long)_hostname;
      |                                         ^
protocols/dns.c:775:62: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
  775 |       unsigned long first_element_len = (unsigned long)dot - (unsigned long)_hostname;
      |
```
```
In file included from ndpi_bitmap64.c:31:
third_party/include/binaryfusefilter.h: In function ‘binary_fuse8_hash’:
third_party/include/binaryfusefilter.h:160:32: error: left shift count >= width of type [-Werror=shift-count-overflow]
  160 |     uint64_t hh = hash & ((1UL << 36) - 1);
```
```
In function ‘ndpi_match_custom_category’,
    inlined from ‘ndpi_fill_protocol_category.part.0’ at ndpi_main.c:7056:16:
ndpi_main.c:3419:3: error: ‘strncpy’ specified bound depends on the length of the source argument [-Werror=stringop-overflow=]
 3419 |   strncpy(buf, name, name_len);
```

1 files changed, 7 insertions, 0 deletions

diff --git a/src/lib/ndpi_domain_classify.c b/src/lib/ndpi_domain_classify.c
index fa866f32d..f1a319067 100644
--- a/src/lib/ndpi_domain_classify.c
+++ b/src/lib/ndpi_domain_classify.c
@@ -47,6 +47,9 @@ ndpi_domain_classify* ndpi_domain_classify_alloc() {
 void ndpi_domain_classify_free(ndpi_domain_classify *s) {
   u_int32_t i;
 
+  if(!s)
+    return;
+
   for(i=0; i<MAX_NUM_NDPI_DOMAIN_CLASSIFICATIONS; i++) {
     if(s->classes[i].domains != NULL) {
       ndpi_bitmap64_free(s->classes[i].domains);
@@ -90,6 +93,8 @@ bool ndpi_domain_classify_add(ndpi_domain_classify *s,
     } else if(s->classes[i].class_id == 0) {
       s->classes[i].class_id = class_id;
       s->classes[i].domains  = ndpi_bitmap64_alloc();
+      if(!s->classes[i].domains)
+        s->classes[i].class_id = 0;
       break;
     }
   }
@@ -117,6 +122,8 @@ u_int32_t ndpi_domain_classify_add_domains(ndpi_domain_classify *s,
     } else if(s->classes[i].class_id == 0) {
       s->classes[i].class_id = class_id;
       s->classes[i].domains  = ndpi_bitmap64_alloc();
+      if(!s->classes[i].domains)
+        s->classes[i].class_id = 0;
       break;
     }
   }