Cloud and initial window improvements.

[ADDED]     Advanced option to mark self as corrupt.
[ADDED]     Tell user initial cloud sync can take a moment.
[IMPROVED]  Initial window now visible on full-screen spaces.
[FIXED]     User name label.

MasterPassword/ObjC/MPAppDelegate_Key.m

@@ -75,6 +75,8 @@ static NSDictionary *keyQuery(MPUserEntity *user) {
 
     if (password)
     NSAssert(![NSThread isMainThread], @"Computing key must not happen from the main thread.");
+    if (!user)
+        return NO;
 
     MPKey *tryKey = nil;