compression: Add and fix null checks

CID #58406, #200016, #58416

(cherry picked from commit 8cfb66b)

modules/compression/compression.c

@@ -1012,7 +1012,8 @@ static int mc_compact_cb(char** buf_p, struct mc_compact_args *mc_compact_args,
 memerr:
  LM_ERR("No more pkg mem\n");
 free_mem:
- free_hdr_mask(hdr_mask);
+ if (hdr_mask != NULL)
+ free_hdr_mask(hdr_mask);
  return -1;
 }
 
@@ -1733,7 +1734,7 @@ static int mc_decompress(struct sip_msg* msg)
  /*If compressed with this module there are great chances that Content-Encoding is last*/
  hdr_vec[3] = msg->last_header;
 
- if (!is_content_encoding(hdr_vec[3])) {
+ if (hdr_vec[3] && !is_content_encoding(hdr_vec[3])) {
  hdr_vec[3] = NULL;
  for (hf = msg->headers; hf; hf = hf->next) {
  if (is_content_encoding(hf)) {

modules/compression/gz_helpers.c

@@ -79,7 +79,7 @@ int gzip_compress(unsigned char* in, unsigned long ilen, str* out, unsigned long
  if (!out->s) {
  out->s = pkg_malloc(neededSize);
  out->len = neededSize;
- if (!out)
+ if (!out->s)
  goto memerr;
  } else if (ilen > out->len) {
  out->s = pkg_realloc(out->s, neededSize);