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, 15 insertions, 0 deletions

diff --git a/src/lib/ndpi_bitmap64.c b/src/lib/ndpi_bitmap64.c
index 1c8368b29..f254c1483 100644
--- a/src/lib/ndpi_bitmap64.c
+++ b/src/lib/ndpi_bitmap64.c
@@ -76,6 +76,9 @@ bool ndpi_bitmap64_compress(ndpi_bitmap64 *_b) {
   ndpi_bitmap64_t *b = (ndpi_bitmap64_t*)_b;
   u_int32_t i;
 
+  if(!b)
+    return(false);
+
   if(b->num_used_entries > 0) {
     if(b->num_used_entries > 1)
       qsort(b->entries, b->num_used_entries,
@@ -122,6 +125,9 @@ bool ndpi_bitmap64_compress(ndpi_bitmap64 *_b) {
 bool ndpi_bitmap64_set(ndpi_bitmap64 *_b, u_int64_t value) {
   ndpi_bitmap64_t *b = (ndpi_bitmap64_t*)_b;
 
+  if(!b)
+    return(false);
+
   if(b->is_compressed) {
     /*
       We need to discard the filter and start over as this
@@ -155,6 +161,9 @@ bool ndpi_bitmap64_set(ndpi_bitmap64 *_b, u_int64_t value) {
 bool ndpi_bitmap64_isset(ndpi_bitmap64 *_b, u_int64_t value) {
   ndpi_bitmap64_t *b = (ndpi_bitmap64_t*)_b;
 
+  if(!b)
+    return(false);
+
   if(!b->is_compressed) ndpi_bitmap64_compress(b);
 
   return(binary_fuse16_contain(value, &b->bitmap));
@@ -165,6 +174,9 @@ bool ndpi_bitmap64_isset(ndpi_bitmap64 *_b, u_int64_t value) {
 void ndpi_bitmap64_free(ndpi_bitmap64 *_b) {
   ndpi_bitmap64_t *b = (ndpi_bitmap64_t*)_b;
 
+  if(!b)
+    return;
+
   if(b->entries)        ndpi_free(b->entries);
 
   if(b->is_compressed)
@@ -178,5 +190,8 @@ void ndpi_bitmap64_free(ndpi_bitmap64 *_b) {
 u_int32_t ndpi_bitmap64_size(ndpi_bitmap64 *_b) {
   ndpi_bitmap64_t *b = (ndpi_bitmap64_t*)_b;
 
+  if(!b)
+    return(0);
+
   return(sizeof(ndpi_bitmap64) + binary_fuse16_size_in_bytes(&b->bitmap));
 }