Fix. Handle new return code for curl_formget in libcurl 7.56.0

Author: moteus

src/lchttppost.c

@@ -44,6 +44,15 @@ static const char *LCURL_HTTPPOST = LCURL_HTTPPOST_NAME;
 # define LCURL_LEN_TYPE long
 #endif
 
+/* 7.56.0 changed code for `curl_formget` if callback abort write 
+ * not sure is it bug or not so set only for single version 
+ **/
+#if LCURL_CURL_VER_GE(7,56,0) && !LCURL_CURL_VER_GE(7,56,1)
+#  define LCURL_GET_CB_ERROR CURLE_READ_ERROR
+#else
+#  define LCURL_GET_CB_ERROR (CURLcode)-1
+#endif
+
 //{ stream
 
 static lcurl_hpost_stream_t *lcurl_hpost_stream_add(lua_State *L, lcurl_hpost_t *p){
@@ -525,7 +534,7 @@ static int lcurl_hpost_get(lua_State *L){
     return lua_error(L);
   }
 
-  if((CURLcode)-1 == code){
+  if(LCURL_GET_CB_ERROR == code){
     if(((lua_gettop(L) == top+1))&&(lua_isstring(L, -1))){
       return lua_error(L);
     }