tool_parse_cfg: Avoid 2 fopen() for WIN32

Using the memdebug.h mem-leak feature, I noticed 2 calls like:
  FILE tool_parsecfg.c:70 fopen("c:\Users\Gisle\AppData\Roaming\_curlrc","rt")
  FILE tool_parsecfg.c:114 fopen("c:\Users\Gisle\AppData\Roaming\_curlrc","rt") 

No need for 'fopen(), 'fclose()' and a 'fopen()' yet again.