Bug#25222 Win32 HANDLE leak in my_sopen()

- When attempting to associate a Windows File handle to a C run-time file
handle there is an upper bound.  Once reached, the newly created handles
will cause a memory leak since they are not properly associated with a
handle that can later be cleaned up.

mysys/my_open.c

@@ -345,7 +345,12 @@ File my_sopen(const char *path, int oflag, int shflag, int pmode)
     return -1;                      /* return error to caller */
   }
 
-  fh= _open_osfhandle((intptr_t)osfh, oflag & (_O_APPEND | _O_RDONLY | _O_TEXT));
+  if ((fh= _open_osfhandle((intptr_t)osfh, 
+                           oflag & (_O_APPEND | _O_RDONLY | _O_TEXT))) == -1)
+  {
+    _dosmaperr(GetLastError());     /* map error */
+    CloseHandle(osfh);
+  }
 
   return fh;                        /* return handle */
 }