libssh2: use calloc as alloc function for libssh2 versions older than 1.3

This workarounds old libssh2 versions not properly initializing
some ssh session variables, which would trigger memory debuggers
warnings on memory being used without having been initialized.

lib/ssh.c

@@ -111,6 +111,7 @@
 /* Local functions: */
 static const char *sftp_libssh2_strerror(unsigned long err);
 static LIBSSH2_ALLOC_FUNC(my_libssh2_malloc);
+static LIBSSH2_ALLOC_FUNC(my_libssh2_calloc);
 static LIBSSH2_REALLOC_FUNC(my_libssh2_realloc);
 static LIBSSH2_FREE_FUNC(my_libssh2_free);
 
@@ -198,6 +199,44 @@ const struct Curl_handler Curl_handler_sftp = {
 };
 
 
+static void
+libssh2_version_components(int *major, int *minor, int *patch)
+{
+  char buff[80];
+  char *ptr = &buff[0];
+  *major = 0;
+  *minor = 0;
+  *patch = 0;
+#ifdef HAVE_LIBSSH2_VERSION
+  /* run-time version */
+  snprintf(buff, sizeof(buff), "%s", libssh2_version(0));
+#else
+  /* compile-time version */
+  snprintf(buff, sizeof(buff), "%s", LIBSSH2_VERSION);
+#endif
+  while(ptr && ISDIGIT(*ptr)) {
+    *major *= 10;
+    *major += *ptr - '0';
+    ptr++;
+  }
+  if(*ptr == '.') {
+    ptr++;
+    while(ptr && ISDIGIT(*ptr)) {
+      *minor *= 10;
+      *minor += *ptr - '0';
+      ptr++;
+    }
+    if(*ptr == '.') {
+      ptr++;
+      while(ptr && ISDIGIT(*ptr)) {
+        *patch *= 10;
+        *patch += *ptr - '0';
+        ptr++;
+      }
+    }
+  }
+}
+
 static void
 kbd_callback(const char *name, int name_len, const char *instruction,
              int instruction_len, int num_prompts,
@@ -305,6 +344,12 @@ static LIBSSH2_ALLOC_FUNC(my_libssh2_malloc)
   return malloc(count);
 }
 
+static LIBSSH2_ALLOC_FUNC(my_libssh2_calloc)
+{
+  (void)abstract; /* arg not used */
+  return calloc(1, count);
+}
+
 static LIBSSH2_REALLOC_FUNC(my_libssh2_realloc)
 {
   (void)abstract; /* arg not used */
@@ -2625,6 +2670,9 @@ static CURLcode ssh_connect(struct connectdata *conn, bool *done)
 #endif
   struct ssh_conn *ssh;
   CURLcode result;
+  int major = 0;
+  int minor = 0;
+  int patch = 0;
   struct SessionHandle *data = conn->data;
 
   /* We default to persistent connections. We set this already in this connect
@@ -2659,9 +2707,15 @@ static CURLcode ssh_connect(struct connectdata *conn, bool *done)
   sock = conn->sock[FIRSTSOCKET];
 #endif /* CURL_LIBSSH2_DEBUG */
 
-  ssh->ssh_session = libssh2_session_init_ex(my_libssh2_malloc,
-                                             my_libssh2_free,
-                                             my_libssh2_realloc, conn);
+  libssh2_version_components(&major, &minor, &patch);
+  if((major < 1) || ((major == 1) && (minor < 3)))
+    ssh->ssh_session = libssh2_session_init_ex(my_libssh2_calloc,
+                                               my_libssh2_free,
+                                               my_libssh2_realloc, conn);
+  else
+    ssh->ssh_session = libssh2_session_init_ex(my_libssh2_malloc,
+                                               my_libssh2_free,
+                                               my_libssh2_realloc, conn);
   if(ssh->ssh_session == NULL) {
     failf(data, "Failure initialising ssh session");
     return CURLE_FAILED_INIT;