ssl: reduce allocate space for ssl backend when FTP is not supported.

[MAntoniak]

Additionally, adding a backend check for NULL everywhere

[bagder]

I'm not a total fan of how this turns one malloc into four for a regular build. How about instead making the function similar to this? (untested)

static struct connectdata *allocate_conn(struct Curl_easy *data)
{
  struct connectdata *conn = calloc(1, sizeof(struct connectdata));
  if(!conn)
    return NULL;

#ifdef USE_SSL
  /* The SSL backend-specific data (ssl_backend_data) objects are allocated as
     a separate array to ensure suitable alignment.
     Note that these backend pointers can be swapped by vtls (eg ssl backend
     data becomes proxy backend data). */
  {
    size_t onesize = Curl_ssl->sizeof_ssl_backend_data;
    size_t totalsize = onesize;
    void *ptr;
    bool allocate_result = true;

#ifndef CURL_DISABLE_FTP
    totalsize *= 2;
#endif
#ifndef CURL_DISABLE_PROXY
    totalsize *= 2;
#endif

    conn->ssl[FIRSTSOCKET].backend = ptr = calloc(1, totalsize);
    if(!ptr)
      return NULL;
#ifndef CURL_DISABLE_FTP
    conn->ssl[SECONDARYSOCKET].backend = ptr += onesize;
#endif
#ifndef CURL_DISABLE_PROXY
    conn->proxy_ssl[FIRSTSOCKET].backend = ptr += onesize;
#ifndef CURL_DISABLE_FTP
    conn->proxy_ssl[SECONDARYSOCKET].backend = ptr += onesize;
#endif
#endif
  }
#endif

[MAntoniak]

I have modified the memory allocation as you wrote.

[bagder]

I think you should remove != NULL from these checks, as we normally check pointers for being non-NULL like that everywhere else.

[bagder]

This is the first of 4 compiler warnings because you add the assert before the last variable declaration:

vtls/openssl.c:1872:3: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]

[bagder]

Thanks!