client: Fix settings upgrade missing some steps

client: Fix settings upgrade missing some steps

Remove cache check in Settings::localKeyExists().  This fixes
settings version upgrade wrongly skipping some steps due to earlier
migration steps causing default values (not stored in .conf) to be
loaded into settings cache.  Most notably, creating/writing the
QtUiStyle settings Qt StyleSheet.

The symptoms are only visible when migrating multiple steps at once,
hence not catching this earlier.

Bug originally introduced in d2ac8f78a0e050d2efa397c434b249d6b3391576