wininet: Don't bother reconnecting to server for compat secure mode if we don't have compat cred handle.

This prevents stale drawing from being revealed if the window later grows.

For instance, 19 ppem "VL Gothic" on Windows, the advance value is 10
for half-width characters, but 18 for full-width characters.  In this
case, tmAveCharWidth is 9. Thus using tmAveCharWidth is reasonable.