lib: strndup/memdup instead of malloc, memcpy and null-terminate

- bufref: use strndup
 - cookie: use strndup
 - formdata: use strndup
 - ftp: use strndup
 - gtls: use aprintf instead of malloc + strcpy * 2
 - http: use strndup
 - mbedtls: use strndup
 - md4: use memdup
 - ntlm: use memdup
 - ntlm_sspi: use strndup
 - pingpong: use memdup
 - rtsp: use strndup instead of malloc, memcpy and null-terminate
 - sectransp: use strndup
 - socks_gssapi.c: use memdup
 - vtls: use dynbuf instead of malloc, snprintf and memcpy
 - vtls: use strdup instead of malloc + memcpy
 - wolfssh: use strndup

Closes #12453

lib/md4.c

@@ -194,11 +194,9 @@ static int MD4_Init(MD4_CTX *ctx)
 static void MD4_Update(MD4_CTX *ctx, const void *data, unsigned long size)
 {
   if(!ctx->data) {
-    ctx->data = malloc(size);
-    if(ctx->data) {
-      memcpy(ctx->data, data, size);
+    ctx->data = Curl_memdup(data, size);
+    if(ctx->data)
       ctx->size = size;
-    }
   }
 }