wininet: Don't close the connection if the caller passes in zero for the number of bytes to be read.

Only close the connection when the bytes read equals the content length.

Fixup HTTP_DrainContent, which relied on the previous incorrect 
behaviour to instead close connections with no content length manually.

dlls/wininet/http.c

@@ -738,6 +738,12 @@ BOOL WINAPI HttpAddRequestHeadersA(HINTERNET hHttpRequest,
 static void HTTP_DrainContent(LPWININETHTTPREQW lpwhr)
 {
     DWORD bytes_read;
+
+    if (!NETCON_connected(&lpwhr->netConnection)) return;
+
+    if (lpwhr->dwContentLength == -1)
+        NETCON_close(&lpwhr->netConnection);
+
     do
     {
         char buffer[2048];

dlls/wininet/internet.c

@@ -1724,7 +1724,7 @@ BOOL INTERNET_ReadFile(LPWININETHANDLEHEADER lpwh, LPVOID lpBuffer,
             {
                 lpwhr->dwContentRead += bytes_read;
                 *pdwNumOfBytesRead = bytes_read;
-                if (!bytes_read)
+                if (!bytes_read && (lpwhr->dwContentRead == lpwhr->dwContentLength))
                     retval = HTTP_FinishedReading(lpwhr);
                 else
                     retval = TRUE;

dlls/wininet/tests/http.c

@@ -444,6 +444,7 @@ static void InternetReadFileExA_test(int flags)
 
         length += inetbuffers.dwBufferLength;
     }
+    ok(length > 0, "failed to read any of the document\n");
     trace("Finished. Read %d bytes\n", length);
 
 abort: